Traffic Crash
Investigations
A Training Guide for
Law Enforcement Officers
Wisconsin Department of Justice
Law Enforcement Standards Board
December 2009
The Law Enforcement Standards Board approved this textbook
on December 1st, 2009.
Training Academy effective date is May 1, 2010.
All law enforcement basic preparatory training courses that begin on or after May 1st,
2010, must incorporate this updated textbook and any related updates to the curriculum.
Courses beginning before that date may elect to use these updated materials.
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December 2009
ACKNOWLEDGEMENTS
Many people have contributed to the writing of this manual. The Training and
Standards Bureau, Wisconsin Department of Justice gratefully acknowledges the
dedication of the Patrol Procedures Advisory Committee, which has worked long
and hard to revise the content of earlier manuals and develop new content for the
present guide. The current members of the Committee are:
Designated Representatives
Jeff Pettis, Sheriff’s Representative
Tom Winscher, Chief’s Representative
Clark Pagel, Wisconsin Technical College System
Paul Matl, Wisconsin State Patrol
Craig Henry and Chance Bamba, Milwaukee Police Department
Doug Funk, Milwaukee County Sheriff’s Office
Sherri Strand, Madison Police Department
Stephanie Pederson, Training and Standards Bureau (Chair)
Practitioners
Monica Barman, Sun Prairie Police Department
Bruce Buchholtz, Platteville Police Department
Steven D. Hausner, Burlington Police Department
Ken Pileggi, Mukwonago Police Department
Deanna Reilly, Madison Police Department
Tom Witczak, Fox Valley Technical College
Hammond, Ken, Training and Standards Bureau
Emeritus (non-voting) Members
Colleen Belongea
Timothy Hufschmid
Jay Iding
Bernie Kocher
Dave Mattheisen
Robert Miller
Mike Murray
Richard Nichols
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TABLE OF CONTENTS
INTRODUCTION .............................................................................................................. 1
TRAFFIC CRASH INVESTIGATION ................................................................. 1
Levels of Investigation ............................................................................................. 2
At-Scene Investigation ............................................................................................ 2
Advanced (Technical) Investigation ...................................................................... 2
Collision Reconstruction .......................................................................................... 4
Traffic Crash Investigation ...................................................................................... 4
Investigator Qualities ............................................................................................... 5
INVESTIGATING CRASHES ......................................................................................... 7
REQUIREMENTS OF REPORTING CRASHES ............................................... 7
Wisconsin Statutes Regarding Accidents and Accident Reporting .................. 7
RESPONDING TO CRASHES ........................................................................ 10
Incident Response ................................................................................................. 10
RESPONDING TO THE SCENE (Report) ....................................................... 11
Arriving at the Scene ............................................................................................. 11
EVALUATION OF THE SCENE (Evaluate) ..................................................... 12
SCENE STABILIZATION (Stabilize) ................................................................ 12
PRESERVE LIFE AND EVIDENCE AT THE SCENE (Preserve) .................... 14
Operator, Passenger, and Witness Interviews .................................................. 14
Vehicle and Occupant Restraint System Inspection ........................................ 16
MECHANICS OF MEASURING AND DOCUMENTING CRASH SCENES ........ 19
MEASURE AND DOCUMENT THE CRASH SCENE (Organize).................... 19
Results at a Crash Scene ..................................................................................... 20
Vehicle Position ...................................................................................................... 20
Debris areas ............................................................................................................ 20
Road Marks ............................................................................................................. 23
Meanings of Marks ................................................................................................. 30
LOCATING SPOTS FOR EACH RESULT ...................................................... 30
MEASUREMENT SYSTEMS .......................................................................... 32
Coordinate System................................................................................................. 32
Triangulation System ............................................................................................. 34
Combination of Systems ....................................................................................... 36
MARKING SPOTS ON THE ROAD AND ROADSIDE .................................... 37
Marking Supplies .................................................................................................... 37
Marking Spots ......................................................................................................... 37
CRASH SCENE DIAGRAMS AND SKETCHES.............................................. 39
Field Sketch............................................................................................................. 39
Labeling ................................................................................................................... 43
RECORDING BASIC MEASUREMENTS ....................................................... 46
Table of Measurements ........................................................................................ 46
MEASURING................................................................................................... 47
Measuring Devices................................................................................................. 48
Using Measuring Tapes ........................................................................................ 49
Reading Tapes and Recording Measurements ................................................. 50
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Electronic Measuring Devices .............................................................................. 51
ADDITIONAL AND SUPPLEMENTAL MEASUREMENTS ............................. 52
LABELING AND REVIEWING THE FIELD SKETCH ...................................... 53
AFTER-COLLISION SITUATION MAPS (SCALE DIAGRAM) ........................ 53
Templates ................................................................................................................ 54
Return the Scene to Normal (Normalize) ........................................................... 55
SUMMARY ...................................................................................................... 56
WISCONSIN MOTOR VEHICLE ACCIDENT REPORT ......................................... 59
OVERVIEW OF WISCONSIN ACCIDENT REPORTS (Document and Debrief)
........................................................................................................................ 59
Wisconsin Motor Vehicle Accident Report Form (MV4000) ............................ 59
Driver Report of Accident Form (MV4002) ......................................................... 67
Badger TraCS and the MV4000 .......................................................................... 69
DRIVER, VEHICLE, ROADWAY, AND ENVIRONMENTAL CONDITIONS AND
FACTORS PRIOR TO THE COLLISION ......................................................... 71
Driver Condition ...................................................................................................... 71
Roadway Conditions .............................................................................................. 71
Environmental Conditions. .................................................................................... 73
CONTRIBUTING CIRCUMSTANCES TO A CRASH ...................................... 73
Driver Factors ......................................................................................................... 74
Vehicle Factors ....................................................................................................... 74
Highway ................................................................................................................... 74
SUMMARY ...................................................................................................... 74
PHOTOGRAPHING THE SCENE ............................................................................... 77
CRASH SCENE PHOTOGRAPHY.................................................................. 77
“AT SCENE” PHOTOS .................................................................................... 78
Basic “At-Scene” Photos ....................................................................................... 78
Photographing Vehicle Damage .......................................................................... 80
Procedures for Photographing a Crash Scene.................................................. 81
OTHER CONDITIONS DEALING WITH PHOTOGRAPHY ............................. 82
TIPS/Techniques .................................................................................................... 82
SUMMARY ...................................................................................................... 83
APPROPRIATE ENFORCEMENT ACTIONS........................................................... 85
PROCEDURES TO DETERMINE SPEED ESTIMATES ................................. 85
ENFORCEMENT ACTIONS ............................................................................ 85
ENFORCEMENT DECISION .......................................................................... 86
OPTION #1: No Formal Enforcement Action.................................................... 86
OPTION #2: Issue a Traffic Citation .................................................................. 86
OPTION #3: Criminal Violations ......................................................................... 87
Non-Contributing Violations .................................................................................. 87
HIT-AND-RUN INVESTIGATIONS .................................................................. 88
SUMMARY ...................................................................................................................... 90
APPENDIX A - GLOSSARY ........................................................................................ 91
APPENDIX B - Wisconsin 2008 Traffic Crash Figures ..................................... 103
APPENDIX C – SLIDE-TO-STOP SPEED ESTIMATES ...................................... 105
REFERENCES ............................................................................................................. 107
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INTRODUCTION
TRAFFIC CRASH INVESTIGATION
Our entire nation is a “nation on wheels.” Over 188 million motor vehicles and
more than 170 million licensed drivers travel over two trillion miles a year on our
streets and highways. 1 Hazardous materials are transported on these roads
every day and thousands of people are killed in crashes on our streets and
highways every year. Traffic jams and delays caused by traffic crashes during
rush hour result in millions of dollars and hundreds of thousands of productive
hours lost to the economy and unnecessary environmental pollution each year.
In 2008, 37,261 people were killed in the estimated 5,811,000 police reported
motor vehicle traffic crashes, 1,630,000 people were injured, and 4,146,000
crashes involved property damage only.2 Since more people are killed and
injured and more economic loss is suffered due to traffic crashes then all other
types of crashes combined, the importance of traffic crash investigation cannot
be overstated. The objective of this type of investigation ranges from providing
the basic police functions, the protection of life and property, to restoring the flow
of traffic.
A vehicle collision, regardless of driver intent, is referred to as a “crash” because
the primary cause or causes typically result from specific driver actions. Traffic
crashes are not accidents; they are avoidable events caused by a single variable
or chain of variables.
There are three basic elements involved in any crash. The first is people. This
includes, but is not limited to experience, impairment, and actions. The second is
vehicles which includes, but is not limited to, size and equipment. The third and
final element is the roadway. It also includes, but is not limited to weather (wet,
dry, snow) and road conditions (road construction, debris). The investigating
officer of the crash will have to locate and preserve any evidence from the
collision found in or on the roadway.
Traffic crashes are extremely confusing events. How they occur, who or what
caused them, and why they occurred are facts law enforcement must determine.
Every officer must know the fundamentals of traffic crash investigation and know
how to prepare traffic crash reports. Law enforcement officers spend a lot of time
responding to, managing and investigating crash scenes. The Wisconsin
MV4000 Report officially records events surrounding a crash. The accuracy and
completeness of the report will depend on the quality of an officer’s investigation
and his/her attention to detail. This area of instruction will introduce you to the
1
2
The Highway Safety Desk Book
NHTSA Traffic Safety Facts (June 2009)
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necessity for accurate, impartial and professional traffic crash investigation and
reporting.
Each subsequent level of investigation relies heavily on the quality of the initial
investigation. The location of the crash, road conditions at the time of the crash,
and other evidence at the scene cannot be replaced or recreated, unless
documented by the officer during the at-scene investigation. The public,
insurance adjusters, the Department of Motor Vehicles, and other involved
personnel will see the results of the crash investigations. The quality of an
officer’s work will reflect directly upon him/her as the investigator and on their
agency.
Levels of Investigation3
The severity and circumstances of a collision will determine the proper level of
investigation. In their order of complexity, the levels are usually called at-scene
investigation, advanced (technical) investigation, and reconstruction.
At-Scene Investigation
The first level of investigation is the at-scene investigation. When a basic crash
occurs, the first responding officer will conduct this level of investigation and file a
standard crash report. The at-scene investigator will collect evidence and
document the scene.
The officer’s first task is to make the scene safe and prevent a second crash.
Traffic must immediately be redirected. Next the officer must care for the injured
and request additional resources if needed. Finally the officer will observe and
record the facts pertaining to the collision. These include taking measurements,
documenting other evidence at the scene, and completing a field sketch. The
investigation may include taking photographs, checking all drivers for intoxication
or other impairment, completing a Wisconsin Motor Vehicle Accident Report
(MV4000) form, and other investigative reporting and documentation. The atscene investigation is primarily concerned with data gathering and recording the
scene.
Advanced (Technical) Investigation
At-scene investigations should be conducted for every collision. Advanced
investigations are undertaken whenever the data obtained at the at-scene level is
insufficient to complete the investigation. The purpose of the advanced
investigation is to collect additional data for determining the charges to be
brought against one or more of the individuals involved, for litigation reasons, or
for laying the foundation for the next level of investigation – reconstruction.
3
International Association of Chiefs of Police. (September 2004) Highway Safety Desk Book: Traffic
Collisions. p. 7-1 – 7-11.
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December 2009
Unlike the at-scene investigation, which is initiated immediately or as soon as
practicable after the collision, the advanced investigation may take place at a
later time. Data from the at-scene investigation will be reviewed. Since much of
the evidence at the scene may already have disappeared, the advanced
investigation may depend heavily on the completeness and accuracy of the data
recorded in the at-scene investigation.
During the advanced investigation the investigator is expected:

To determine the drag factor of the skid surface(s) and the minimum initial
speed of each vehicle (unless already calculated in the at-scene
investigation);

To determine time-distance relationships and solve momentum problems;

To match marks on the roadway with the parts on the vehicle causing
damage, to determine the point of impact;

To determine what is impact damage to the vehicle and what is contact
damage;

To match the damaged areas of the vehicles to determine the principal
direction of force (PDOF);

To correlate injuries with the parts of the vehicle impacted by the
occupants (occupant kinematics);

To determine if headlamps and other lamps were ON or OFF at impact;

To determine if any fire damage occurred before or after impact;

To determine if mechanical or electrical failure contributed to the crash
(this may require the help of a specialist); and

To prepare a scale drawing of the scene from measurements and notes
made at the scene.
Officers need to attend advanced training to learn the techniques used by the
advanced investigator. A perquisite is usually the completion of a basic collision
investigation course or several years of practical experience in at-scene
investigation.
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Collision Reconstruction
Reconstruction is the highest of the three major levels of investigation and is
usually undertaken only in support of litigation or research. Its main purpose is to
determine how the collision occurred. It deals primarily with direct and immediate
causes of the crash. These frequently entail behavioral errors on the part of the
drivers.
Reconstruction expands on all the principles of at-scene and advanced
investigation. It may involve experiments to ascertain performance and other
capabilities of the vehicle, or to determine driver and pedestrian behavior.
Reconstruction entails assembling all the technical data required to build a case
for court.
Although a reconstructionist usually has greater depths of knowledge and
broader experience than an investigator qualified only in at-scene or advanced
investigations and can make more inferences from existing data, he/she is very
dependent on the thoroughness and quality of the investigations conducted at
the scene, and may have to work largely with the evidence that has been
preserved and recorded earlier.
Traffic Crash Investigation
It is important to respond to crashes and to prevent further collisions. Your basic
function as the responding officer is the protection of life and property. As the
first responder, you have to protect your life as the top priority when responding
to crashes. If you do not respond to the scene safely and protect yourself and
the scene, you are of no value to anyone.
Often officers raise the objection that crash investigations merely do the job of
the insurance companies. While it is certainly true that the insurance companies
benefit from a good investigation, the fact that a traffic and/or criminal law may
have been broken puts the responsibility directly in the lap of law enforcement to
gather evidence for prosecution.
You have a responsibility to properly record all of the facts surrounding the crash.
You may well be the only emotionally and financially detached person on the
scene; therefore, your report of the event is logically the most accurate rendition
of the event. All conclusions and any enforcement action you take must be
based on the facts, evidence, and statements you personally gather or know to
be true.
During the crash investigation, you have to determine the cause or causes of the
collision. While the train of thought is that placing blame is not an objective of
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crash investigation, determining the cause or causes may in fact determine who
bore the responsibility for the event.
Investigator Qualities
The qualities of a good crash investigator are those traits, both personal and
professional, that the officer displays on each scene. You must be enthusiastic,
sincere, responsible, and impartial when investigating a crash. You will find that
traffic crash investigation, in real life, will sometimes be a fairly unpleasant task.
Seldom will the people involved in the crash have anything to be happy about.
However, the information in your reports may be useful in preventing future
crashes through the application of education, engineering and enforcement.
Some of the qualities you need to exhibit while investigating a crash will assist
you in effectively completing the investigation while presenting a professional
image of the law enforcement profession.
Many crashes occur in bad weather, resulting in you having to work while
standing in the rain, bitter cold, or extreme heat. Through it all, you must not
make a mistake or fail to carry out your assigned duties. The citizens you will be
working with at the scene may be emotional, some may be rude, or they may be
obnoxious. Because you are human, your initial response may be to lash out in
anger, however, as a professional officer, you must try to rise above your
frustration and anger and realize that this is an upsetting situation for the people
involved in the crash.
You need to investigate all crashes thoroughly no matter how minor. It is easy
for an officer to procrastinate and do the minimum acceptable on minor crashes.
This is unacceptable to the people we serve. To the people involved, our
customers, this is a very traumatic event. A motor vehicle is one of the single
largest investments in many people’s lives and a major purchase to all. You
need to show sincerity to the parties involved. For the people involved in a
crash, this may be one of a very few contacts with law enforcement. You have it
within your power to reap public support or lose it based on the level of
professionalism you display.
Some important habits good investigators adopt include:






Be specific. Do not guess or estimate if measurements can be made.
Evaluate what people say and distinguish fact from opinion. One hard
fact is worth a score of theories, conclusions, opinions, and inferences.
Make personal observations and do not expect to learn all about the
collision from what people say.
Write down information at the time and do not depend on memory.
Write well enough so there will be no need for copying later.
Take advantage of opportunities to get facts and avoid thinking, “I’ll get
that later,” because later is often too late.
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Prepare yourself for responding to traffic crashes before they happen. Some
things you can do to prepare yourself include:

Know the territory. It is important to get to the scene of a collision
quickly. Therefore keep maps, street guides or other directional aids
handy. If you have firsthand knowledge of the roads in the area, that’s
even better.

Learn what and where various organizations are who may have specific
responsibilities with respect to collisions. Know the location of hospitals,
towing services, and fire departments. A list of these, together with
phone numbers and hours of the day in which their services are
available is helpful and it is a good idea to become acquainted with
some of the people in these organizations.

Acquaint yourself with other specialists who may be called to help
investigate a crash scene (photographers, reconstructionists, etc.).
Also, learn your department policy. If you are dispatched to investigate
a collision, follow policies and rules dictated by your department.
Summary
This text will introduce you to the basic skills and steps to respond to a crash and
begin the investigation at the scene. You will learn the procedure for measuring
and documenting the scene at the first level of investigation; the at-scene
investigation. You will not learn advanced techniques that traffic crash
reconstructionists use, however, the information you learn to collect at the scene
will directly affect any future investigation or reconstruction of the collision.
Crashes, Not Accidents
Traffic crashes are not accidents, but are avoidable events caused by a
single variable or chain of variables. Dedicated to reducing traffic
injuries and fatalities by addressing the factors that cause them, the
Bureau of Transportation Safety coordinates a statewide behavioral
highway safety program.
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INVESTIGATING CRASHES
REQUIREMENTS OF REPORTING CRASHES
There are two types of crashes: reportable crashes and non-reportable crashes.
According to Wis. Stat. 346.70(1) any crash must be reported to law enforcement
when it results in:



Injury or death of a person.
$1,000 or more total damage to property owned by any one person.
Damages of $200.00 or more to government property (except motor
vehicles which must be $1,000 or more)
Note: If any party involved in a traffic crash dies within 30 days of the crash, the
report will be a reportable crash.
If an officer cannot respond to the scene of a reportable crash (for example,
during blizzard conditions when there are too many crashes for officers to
respond to every scene), drivers should be instructed to file a Wisconsin Driver
Report of Accident form (MV4002). This form will be covered in more detail later
in the text. Only one report should be completed on the crash, however. If an
officer completes the MV4000 Wisconsin Motor Vehicle Accident Report, drivers
should not be instructed to complete the MV4002.
Wisconsin Statutes Regarding Accidents and Accident Reporting
The following are Wisconsin State Statutes relating to accident reporting and
obligations of the operators involved in crashes.
346.66 Applicability of sections relating to accidents and accident
reporting. In addition to being applicable upon highways, ss. 346.67 to
346.70 are applicable upon all premises held out to the public for use of
their motor vehicles, all premises provided by employers to employees for
the use of their motor vehicles and all premises provided to tenants of
rental housing buildings of 4 or more units for the uses of their motor
vehicles, whether such premises are publicly or privately owned and
whether or not a fee is charged for the use thereof. These sections do not
apply to private parking areas at farms or single-family residences or t
accidents involving snowmobiles, all-terrain vehicles or vehicles propelled
by human power or drawn by animals.
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346.67 Duty upon striking person or attended or occupied vehicle. (1)
The operator of any vehicle involved in an accident resulting in injury to or
death of any person or in damage to a vehicle which is driven or attended
by any person shall immediately stop such vehicle at the scene of the
accident or as close thereto as possible but shall then forthwith return to
and in every event shall remain at the scene of the accident until the
operator has fulfilled the following requirements:
(a) The operator shall give his or her name, address and the
registration number of the vehicle he or she is driving to the person
struck or to the operator or occupant of or person attending any
vehicle collided with; and
(b) The operator shall, upon request and if available, exhibit his or
her operator’s license to the person struck or to the operator or
occupant of or person attending any vehicle collided with; and
(c) The operator shall render to any person injured in such
accident reasonable assistance, including the carrying, or the
making of arrangements for the carrying, of such person to a
physician, surgeon or hospital for medical or surgical treatment if it
is apparent that such treatment is necessary or if such carrying is
requested by the injured person.
346.69 Duty upon striking property on or adjacent to highway. The
operator of any vehicle involved in an accident resulting only in damage to
fixtures or other property legally upon or adjacent to a highway shall take
reasonable steps to locate and notify the owner or person in charge of
such property of such fact and of the operator’s name and address and of
the registration number of the vehicle the operator is driving and shall
upon request and if available exhibit his or her operator’s license and shall
make report of such accident when and as required in s. 346.70.
346.70 Duty to report accident. (1) Immediate notice of Accident: The
operator of a vehicle involved in an accident resulting in injury to or death
of any person, any damage to state or other government – owned
property, except a state or other government-owned vehicle, to an
apparent extent of $200 or more or total damage to property owned by
any one person or to a stat or other government-owned vehicle to an
apparent extent of $1,000 or more shall immediately by the quickest
means of communication give notice of such accident to the police
department, the sheriff’s department or the traffic department of the county
or municipality in which the accident occurred or to a state traffic patrol
officer. In this subsection, “injury” means injury to a person of a physical
nature resulting in death or the need of first aid or attention by a physician
or surgeon, whether or not first aid or medical or surgical treatment was
actually received; “total damage to property owned by one person” means
the sum total cost of putting the property damaged in the condition it was
before the accident, if repair thereof is practical, and if not practical, the
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December 2009
sum total cost of replacing such property. For purposes of this subsection
if any property which is damaged is held in a form of joint or multiple
ownership, the property shall be considered to be owned by one person.
(2) Written report of accident. Unless a report is made under sub. (4) by
a law enforcement agency, within 10 days after an accident of the type
described in sub. (1), the operator of a vehicle involved in the accident
shall forward a written report of the accident to the department. The
department may accept or require a report of the accident to be filed by an
occupant or the owner in lieu of a report from the operator. Every accident
report required to be made in writing shall be made on the appropriate
form approved by the department and shall contain all of the information
required therein unless not available. The report shall include information
sufficient to enable the department to determine whether the requirements
for deposit of security under s. 344.14 are inapplicable by reason of the
existence of insurance or other exceptions specified in ch. 344.
(3) Who to report when operator unable. Whenever the operator of a
vehicle is physically incapable of giving the notice and making the report
required by subs. (1) and (2), the owner of the vehicle involved in the
accident shall give notice and make the report required by subs. (1) and
(2). If the owner of the vehicle is physically or mentally incapable of giving
the notice and making the report required by subs. (1) and (2), and if there
was another occupant in the vehicle at the time of the accident capable of
giving the notice and making the report, the occupant shall give the notice
and make the report.
(4) Police and traffic agencies to report. (a) Every law enforcement
agency investigating or receiving a report of a traffic accident as described
in sub. (1) shall forward an original written report of the accident or a
report of the accident in an automated format to the department within 10
days after the date of the accident.
346.73 Accident reports not to be used in trial. Notwithstanding s.
346.70(4)(f), accident reports required to be filed with or transmitted to the
department or a county or municipal authority shall not be used as
evidence in any judicial trial, civil or criminal, arising out of an accident,
except that such reports may be used as evidence in any administrative
proceeding conducted by the department. The department shall furnish
upon demand of any person who has or claims to have made such a
report, or upon demand of any court, a certificate showing that a specific
accident report has or has not been made to the department solely to
prove compliance or a failure to comply with the requirements that such a
report be made to the department.
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RESPONDING TO CRASHES
When responding to reported crashes it is important that you remember the
RESPOND acronym. The RESPOND model should be used as a guideline
when responding to a crash scene. Trying to follow a fixed step-by-step
procedure in responding to and investigating a collision can be as bad as having
no plan at all. You must be flexible and respond to those things which need to be
addressed first. You may also be able to accomplish a few steps listed below at
the same time.
Incident Response
R




Report
Become aware
Plan response
Arrive/Assess
Alarm/Inform



Evaluate
Look for dangers
Determine backup needs
Enter when appropriate/tactically sound


Stabilize
Subject(s)
Scene
E
S
P

Preserve
Life
- Conduct an initial medical assessment (as trained)
- Treat to level of training
- Continue to monitor the subject(s)
Evidence



Organize
Coordinate additional responding units (if necessary)
Communicate with dispatch and others
Organize the collection of evidence (if appropriate)



Normalize
Provide long-term monitoring (as appropriate)
Restore scene to normal
Return radio communications to normal


Document/Debrief
Debrief self, other responding personnel, subject(s), other persons
Document incident appropriately

O
N
D
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December 2009
RESPONDING TO THE SCENE (Report)
When you become aware of a crash, plan your response to the scene. Obtain as
much information as you can about the collision. Other information needed
includes:








Location of the collision
Time of occurrence
What is involved
Extent of injury and damage
Obstruction of traffic
Whether fire is involved
Have ambulance, tow truck, fire equipment, and other investigators been
called?
What assistance may be available
Based on this information, plan your route to the scene and consider possible
things to be done upon arrival.
Employ safe driving techniques (drive with “due regard”) when responding and
be aware that your attention may be diverted to thinking about what type of
scene you will arrive at and what type of additional equipment you may need.
You may narrow your peripheral vision, known as tunnel vision, which will
prevent you from being fully aware of your surroundings. This may also occur to
motorists as well as confusion and panic when they see and hear the emergency
lights and siren. Not arriving on the scene due to becoming involved in a crash is
of no value to anyone.
Have the emergency lights and siren activated when requesting the right of way
from other motorists. Using the emergency lights and siren expresses your
intentions to other motorists that the patrol vehicle is in an emergency mode.
When responding, follow the shortest and quickest possible route to the scene.
Arriving at the Scene
When arriving at the scene select a safe location to park the patrol vehicle. You
may need to use the patrol vehicle as a barrier to approaching motorists to
protect the scene, victims and any evidence. The location of the patrol vehicle
should be a safe distance from the vehicles involved and the emergency lighting
should remain activated to warn approaching motorists of the hazard. At night
you should park so the headlights illuminate the entire scene; however, you
should not blind oncoming traffic with the patrol vehicle’s headlights at night.
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December 2009
EVALUATION OF THE SCENE (Evaluate)
Upon arrival at the scene, watch for suspicious vehicles or subjects leaving the
scene. The suspicious activity may be subjects who were involved in the crash
who are fleeing the scene. They may be unlicensed drivers, have been involved
in illegal activities, under the influence, etc. These vehicles may also lead to
witnesses who otherwise would have been unknown.
As you look over the scene, begin to evaluate what challenges the scene
presents. Look for dangers such as hazardous materials, vehicles on fire,
downed power lines, etc. Also, try to determine how many injured people are on
scene. Looking for these dangers and injuries will help you determine if you
need to request any medical support, fire personnel, or other types of resources
to respond to the scene.
Before you enter the scene, you need to evaluate if it is appropriate and safe for
you to enter the scene. If there is a hazardous spill or downed power lines, the
scene may not be safe for you or others to enter the scene, even if there are
injured people. If you are hurt in the process of trying to reach the injured you
will no longer be able to help them. Ensure you request any back-up or
resources needed to make the scene safe, and wait for them to make the scene
safe, before you enter the scene.
SCENE STABILIZATION (Stabilize)
As a first responding officer, you have to set priorities and make decisions at the
scene. The officer in charge of the scene has to stabilize the scene as quickly as
possible to prevent further injury to the people involved in the crash, officers or
other motorists. The primary task you have on the scene is to check all subjects
involved for injuries and provide first aid until more resources arrive on scene.
Severely injured persons should not be moved, except to preserve their safety.
Traffic control is essential at a crash scene to prevent further crashes or injuries.
Rerouting vehicles around the crash scene is the most common procedure used.
Gathering crowds or unnecessary personnel should be cleared from the crash
scene. You may have to request additional officers for crowd control or traffic
direction/diversion at the scene. You may need to request that a utility company
respond to the scene for downed power lines, gas line damage, and other utility
related problems resulting from the crash. Additionally, requests may be made
for tow trucks to remove non-drivable vehicles from the scene.
You may have to request additional equipment and/or officers due to the severity
of the crash scene. The additional officer(s) may be used to close traffic ramps,
intersections or entire roadways, assist in investigating the scene and other
duties due to the crash size and severity of the crash. If the crash is severe, you
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December 2009
may need to contact a crash reconstructionist or an investigator who is trained in
more advanced traffic crash investigations than you are.
Use flares and/or cones to assist in traffic control to maneuver traffic around or
away from the crash site. (Figure 2-1) Use care when placing flares and do not
place them near spilled flammable liquids. If the crash is around a blind curve or
just over the top of a hill, put flares out before passing the view obstruction. You
should also consider placing your vehicle or a second squad on the top of the hill
or entrance into the curve with the emergency lighting on to alert motorists and
give them time to slow down before approaching the crash site. This may be
especially important if, for example, the crash site is immediately over the top of
the hill in severe weather, such as an ice storm or snow storm. If motorists come
to the top of the hill, see the crash site at the last minute, and slam on the brakes,
they may hit ice or snow and lose control of their vehicle causing another crash.
Your responsibility is to stabilize and protect the scene; attempting to create the
least amount of hazard to individuals at the scene as well as to oncoming traffic.
Place warning devices far enough back from the scene to provide the oncoming
motorists time to react properly.
• Angle cones/flares to channel traffic
• Angle squads if more than one (channels drivers and
adds more light to scene)
• Alternate Cones and Flares if you have both
(Figure 2-1)
It is imperative that you and other responding officer(s) recognize the emotional
and psychological effects that may be encountered by both the officer(s) and the
subjects involved. The responding officer(s) must be aware of and prepared to
act accordingly to prevent “becoming part of the problem”. Once at the scene,
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December 2009
you and the other officer(s) must make rapid decisions as to vehicle placement
with respect to protection of life and property and the accessibility of equipment.
If the vehicles are in traffic and can be moved safely, the officer(s) should protect
themselves and the motorists by moving them out of traffic on to the side of the
roadway. This decision would be based on the nature of injuries and damage to
the vehicles involved.
PRESERVE LIFE AND EVIDENCE AT THE SCENE (Preserve)
Once the scene is stabilized, your next step is to preserve life and evidence at
the scene. This includes conducting interviews, inspecting vehicles and
occupant restraint systems, and collecting and photographing other evidence at
the scene.
Operator, Passenger, and Witness Interviews
Begin interviewing the operators, passengers, and witnesses to the crash. Prior
to any of the parties involved in the crash leaving the scene via ambulance,
attempt to obtain a statement as to what occurred. Due to the nature of some
injuries, this may not be possible and the officer will have to interview the injured
party or parties later.
Witnesses should be separated and interviewed separately. Do not allow
witness to gather and exchange their stories about what occurred. Attempt to
interview witnesses as soon as possible after the crash; they are under no legal
obligation to remain at the scene of the crash. It is important that for each person
interviewed you are tactful, patient, and employ good communication skills.
Obtain identification from each person and record the information. Obtain
statements from witnesses both verbally and then, if necessary, obtain a written
statement from the witness. Have the witness sign their statement, as this is
evidence obtained from the scene.
While interviewing, allow the person to tell his or her version of the events without
interruption. Refrain from telling the person being interviewed “what happened.”
Ask the person exactly where they were (their position), when the crash
occurred. This may help to prove or disprove statements made later in the
investigation. While interviewing subjects, pay attention to any signs or actions
that suggest injury, illness, or any impairment.
When interviewing operators be aware of the person’s constitutional rights if the
investigation leads into possible criminal wrongdoing. You may request that the
operator(s) provide a signed written statement after the interview. This may
assist you in future investigations.
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December 2009
When interviewing witnesses regarding the crash it is important to ask the
witness questions regarding:










Their positioning in relationship to the crash prior to the initial impact.
If they observed the signal prior to the crash? Who had the red light?
What did the vehicles do after the crash? Vehicle movement after the
crash.
If they saw anyone flee the scene?
If they saw who was operating which vehicle?
The approximate speed of the vehicle or vehicles involved prior to the
crash.
What was said by any of the operators immediately after the crash?
If they observed any unusual actions by any of the vehicles prior to the
crash?
If a pedestrian was involved, where was the pedestrian prior to the crash?
What was the pedestrian doing? Were they running or walking?
These are some of the typical questions you may want to ask a witness
regarding the crash. You may have more questions depending upon the type of
crash involved.
When questioning the operator(s) some of the basic questions you should ask
include:









Exactly where were you when you first saw the vehicle? (Point of
awareness)
What were you doing at the moment you first saw the other vehicle?
o Movement, speed, direction, speeding up or slowing down, turning,
backing, etc….
o Attention – where were you looking? Talking? Other?
Where were you when you first realized you were in trouble? (Point of
perception)
What were you doing at the moment you realized you were in trouble?
(movement and attention)
Exactly what did you do, if anything, to avoid the crash? (possible evasive
action)
Then what happened? Have the driver describe in his/her own words.
Exactly where did the collision or first harmful event take place? (locate
unless known)
Where did you stop after the collision (final position)
What is the first thing you remember after the crash? (in his/her own
words)
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December 2009

If unconscious – What is the last thing you remember clearly before the
crash?
o Verify story – do not press.
o Establish trip plan as well as degree of shock/amnesia.
o Note time period of unconsciousness.

Who did you first see after the crash (clue to witnesses)
o What did you say to him/her?
This list is not all inclusive, but it gives you a good starting point when asking
operators about the incident. Depending on the circumstances you will have to
ask more questions or may have to ask similar questions to those above, but not
necessarily the exact questions above.
If the crash scene is serious in nature and additional officers are assisting with
the investigation, the officer in charge of the scene should recheck the
information that was obtained from the witnesses prior to the witnesses leaving
the scene. Every officer has a different interviewing technique and he or she
may not record all of the information that they have be informed of by the
witness. This will reduce the follow-up calls that will slow the investigation.
Vehicle and Occupant Restraint System Inspection
There are several ways to identify a motor vehicle to distinguish it from all other
vehicles. Identification is not the same as describing a vehicle as belonging to
some class of vehicles.
A registration number is assigned by the state department of motor vehicles,
displayed on the vehicle by registration plates and recorded on a registration
certificate. Trucks carry additional registration numbers and trucks in interstate
commerce are also registered by a federal agency and carry an ICC number in
addition to a state number. All these can serve as additional items of
identification but they rarely figure in traffic-collision investigations.
The Vehicle Identification Number (VIN) is the number assigned to the vehicle by
the manufacturer primarly for registration and identification purposes. This
number is sometimes called the “serial number” or “body number.” All vehicles,
except for older vehicles, have the number embossed in part of the vehicle. It is
readily visible to an observer standing outside of the vehicle without need of
access to the vehicles interior.
In most cases, the VIN consists of not more than 17 characters stamped into a
metal plate riveted to the deck of the instrument panel at the left side and visible
through the windshield. Sometimes a vehicle is so badly damaged that the VIN
in the usual place cannot be read. If it is important, look for the engine
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December 2009
identification number (EIN) or transmission identification number (TIN). These
may or may not be the same as the VIN.
A careful inspection of vehicle equipment and contents is necessary. Pay
attention to any newly damaged parts of the vehicle and classify the type of
damage. Be aware of old damage that was not caused during the current crash
investigation. Items affecting vehicle control should be particularly checked, such
as tires, brakes, lights, steering, signals and safety equipment. For example, it is
important to know whether a tire blew out as a result of the crash or whether the
tire blowout was a possible contributing factor of the crash.
Two types of damage that can occur on a vehicle:

Contact damage - damage caused by direct contact with some object that
is not a part of the vehicle itself.

Induced damage - damage caused to vehicle parts that did not come in
contact with the object struck, but resulted from the shock of the collision.
All damage observed should closely match objects that came in contact with that
area of the vehicle. If you observe that the damage patterns do not match,
investigate further.
Check for any signs of defective equipment that may have contributed to the
crash. Some drivers may blame malfunctioning vehicle equipment for the crash,
such as brake or tire failure. It is important that if the crash involves a fatality, the
officers at the scene should not touch the brake pedal as they could destroy
evidence from that vehicle without knowing it. That type of investigation should
be left to the trained crash reconstruction officer. Make note of the reported
mechanical defect and relay the information to the reconstructionist. Other
mechanical defects may need to be inspected by a qualified mechanic. Less
than one percent of all crashes are caused by mechanical failure yearly. Take
detailed notes of mechanical failures and note them in your report.
Perform a detailed inspection of the vehicles involved in the crash. They should
be performed to see if the vehicle needs to be removed from the scene by a tow
truck. Inspect the vehicle for tire misalignment, bent suspension parts, fluid
leakage, air bag deployment, broken windshield and other glass, missing
headlights and taillights (if dark outside).
Inspect the interior of the vehicles involved in the crash. The inspection should
include looking for view obstructions, dirty glass, open containers, improper
mechanical devices (illegal steering wheels, pedals, etc.). Contents of the
vehicle may also give important information concerning the identity, residence,
occupation, destination and position of vehicle occupants.
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December 2009
The inspection should also include inspecting the radio. Was the radio volume
turned up very high? If the battery on the vehicle was damaged you may not be
able to check the radio volume. Where was the positioning of the headlight
switch? Was it in the on position, off position or in the parking light mode? The
operator may have been operating with their headlamps off in the evening hours.
Do not turn the switch on or off as evidence in the crash may be destroyed.
Note your initial observation when arriving on the scene.
You should also check for seat belt damage and usage. There may have been
paramedics in the vehicle who removed the seat belts from the victims. Look at
the webbing of the seat belt. Look for stains or markings that would not be on
the seat belt if it were not in use.
Note the location of blood, fluids, dirt and glass. Look for fraying from the guide
loop of the seat belt. The edges may show fraying from use. This may not be
visible if you are looking at a new vehicle. Look to see if the belt buckle is
accessible or is the belt tucked under the seat. Additional seat belt inspection
should be performed by the crash reconstructionist if necessary due to serious
injury or fatality.
Note the general condition of the interior of the vehicle. Were there items that
interfered with the operator’s safe operation of the vehicle? Were there items on
the dash that may have slid off the dash and interfered with the operator’s
operation of the vehicle? Was there a lap top computer operating in the driver’s
compartment? Was there any cell phone in operation and lying in the front seat
area of the vehicle? These are all items that you should be looking for in the
interior of the vehicle. With technological advances, people are operating
vehicles unsafely while using electronic devices.
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December 2009
MECHANICS OF MEASURING AND
DOCUMENTING CRASH SCENES4
MEASURE AND DOCUMENT THE CRASH SCENE (Organize)
After stabilizing the scene, interviewing passengers, drivers, and witnesses, and
checking the vehicles, you will investigate the scene in more detail and document
your findings. This includes taking measurements, photographing the scene, and
completing an Accident Report. The Wisconsin Motor Vehicle Accident Report
Form (MV4000) will be the main form used to document the crash scene. While
it is important to fill this form out completely, you should not use this form to drive
your investigation on scene. Too many officers rely on this form to guide how
they process the scene which may prevent them from doing a thorough
investigation. This section will focus on evidence collection, measuring, drawing
a field sketch, and photographing a crash scene. The Wisconsin Motor Vehicle
Accident Report Form (MV4000) will be discussed a little later in the text.
The extent to which a collision can be reconstructed is dependent upon the
evidence collected at the scene. Measurements taken at the scene are the
foundation for speed estimates and other conclusions as to how the crash
occurred. Your goal at the scene is to document the results of the collision so
that a scale diagram can be drawn from your measurements and evidence
collection. You should follow the steps listed below to process the scene first
and fill out the MV4000 report towards the end of processing the scene.
There are eleven basic steps to follow when measuring and documenting the
crash scene. These steps are:
1. Decide what results of the crash to locate at the scene.
2. Decide what spots must be located for each of the results.
3. Decide which system of measurement is best.
4. Mark spots on the road and roadside.
5. Start a field sketch.
6. Prepare a table for recording basic measurements.
7. Make measurements and enter them into the table.
8. Decide what additional and supplementary measurements are needed.
9. Make additional measurements.
10. Review the field sketch and measurement records for clarity and
completeness.
11. Complete the field sketch by identifying items in the sketch.
4
Baker, Kenneth, S. (2001) Traffic Collision Investigation. This entire section on measuring and
documenting a crash scene is either directly from this source or adapted from Northwestern University
Traffic Institute information.
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December 2009
Results at a Crash Scene
Evidence obtained through interviews and vehicle inspections are only part of the
information that needs to be collected at a crash scene. Investigators cannot rely
on this information alone. Trauma, excited states of emotion, and shock can
cause witnesses and victims to give inaccurate information. In fatal collisions,
there may not be anyone left alive to explain what happened. Additionally,
vehicle evidence may be confusing or hard to understand without looking at other
results, such as damage to surrounding objects or roadway results. The word
result refers to evidence such as debris, marks, damaged objects, vehicles, and
other equipment, etc., at the scene.
You must first decide what results of the crash to locate at the scene. Carefully
examine the scene noting the results of the crash, and any temporary conditions
which may have contributed to the collision. Always be mindful that this may be
the only opportunity to document this evidence. Once the scene is cleaned up
the evidence may be gone forever. Results you should locate include:






The position of each vehicle and any bodies outside of the vehicle(s).
Debris areas: significant vehicle parts and pedestrian possessions;
underbody dirt; liquid spatter, dribble, and puddles; and any other debris
that came from a vehicle involved in the crash.
Scars (gouges and scratches) on the road, roadside, and on fixed
objects.
Tire marks: skid marks, yaw marks, and collision scrubs.
Parked vehicles which may have an obstructed view.
Barricades and construction vehicles or materials.
Vehicle Position
Locate the final resting positions of all of the vehicles involved in the collision.
Treat trailers as a separate vehicle regardless of whether or not it remains
attached to the towing vehicle. For this purpose, motorcycles and bicycles are
also classified as vehicles. Locate the positions of any pedestrians, motorcycle
or bicycle riders, and ejected occupants whether deceased or injured.
Final positions of vehicles or bodies are classified as controlled or uncontrolled.
Uncontrolled final positions are those reached by vehicles or bodies
unintentionally after collisions. Controlled final positions are those to which
vehicles or bodies are moved on purpose after a collision.
Debris areas
Locate debris at the crash scene. Various types of debris include dislodged
vehicle parts and underbody dirt or snow. Liquid debris such as spatter, dribble,
puddles, runoff, and soak-in may be present. Debris in pedestrian collisions may
20
December 2009
also include belongings such as hats, handbags or glasses, as well as blood or
body tissue.
(Debris lying around the crash scenes)
Underbody Debris. Underbody debris in the form of mud, rust, paint, snow and
sometimes gravel, sticks to the underside of fenders, engine body and other
parts. In a collision this debris comes loose in two ways:


The metal to which it is stuck bends or crinkles and debris chips off.
The shock of the collision loosens it.
After a collision, underbody debris may be heaped in a pile or it may be scattered
thinly over a wide area. If the vehicle is moving when underbody debris is
dislodged, the debris is also moving and does not drop straight down on the
ground. It continues to move in the direction the vehicle was moving and at
approximately the vehicle’s speed until it reaches the ground, unless it first
strikes some part of the vehicle moving in another direction because of the
collision. In these cases the debris is redirected. Because debris scatters so
much it is usually a poor indicator of precisely where the collision took place.
Spatter (Vehicle Liquids). Spatter occurs when a vehicle container, such as a
radiator, is collapsed by a collision with the result that liquid squirts out violently
and splashes on the road and nearby vehicle parts. Such spatter areas are dark,
wet spots, irregular in shape, and often composed of or surrounded by many
small spots or “freckles.” Sometimes a lot of spatter makes an elongated
“splash” pattern. Spatter reaches the road before the damaged vehicle moves
very far and it is, therefore, a good indicator of where it was when the collision
collapsed or broke open the liquid container.
Battery acid spatter. If the road is wet, battery acid spatter will not show. After it
dries the spot where the acid struck the pavement may show quite plainly as a
“bleached” area.
Dribble (Vehicle Liquids). Dribble is liquid draining – not squirting from a ruptured
container on a wrecked vehicle. If the vehicle is moving, the dribble marks the
path of the leaking part, usually from the point of maximum engagement to the
final position. Rapid leakage and slow vehicle movement gives a conspicuous
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December 2009
dribble path, sometimes continuous. Slow leakage and fast vehicle movement
give an indistinct dribble path, often just a few scatter drops along the way.
Puddle (Vehicle Liquids). As soon as a vehicle that is dripping liquid stops
moving, the dribble forms a puddle under the leaking part. This puddle shows
where that part of the vehicle stopped. This is especially significant when the
vehicle has been moved before the investigator arrives at the scene.
Run-Off (Vehicle Liquids). Run-off occurs when a puddle forms on sloping
pavement. The liquid draining from the vehicle streams down hill.
Soak-In (Vehicle Liquids). Soak-in occurs where liquid is absorbed by soil or
pavement cracks, either where run-off reaches the road shoulder or where the
puddle forms off the pavement.
Tracking (Vehicle Liquids). Tracking of vehicle liquids results when tires roll
through puddles, run-off, or spatter and, becoming wet, leave tire prints on the
pavement as they roll on.
Liquid Cargo. Liquid cargo, usually from tank trucks, becomes debris when it is
spilled on the road by collision. The position of the liquid cargo rarely makes any
significant point in connection with the collision. If the spilled liquid is flammable,
corrosive, or toxic, damage control may be the overriding consideration. Refer to
the Emergency Response Guidebook when dealing with hazardous materials.
Spatter and dribble help locate collision positions. Dribble and puddles indicate
where vehicles came to rest. Other kinds of liquid debris do not usually help
much in determining how the crash happened.
Vehicle Parts. Compared to liquids which have come from vehicles, other
vehicle parts are seldom significant as debris. Three important exceptions are:

Small parts found at the scene may help identify a vehicle that has left the
crash scene. They may be useful therefore, in hit-and-run investigations.

Whole sections of the vehicle that have broken loose in collisions may be
significant because of their final positions. This is the case when a
vehicle breaks in two in a collision with a tree or when the engine is
knocked out of a vehicle in a collision with a truck. The positions of these
major parts are located by measurements in the same way that final
positions of vehicles themselves are located.

Tempered glass from rear windows of vehicles may shatter into
thousands of popcorn-sized pieces when the glass is broken in a collision.
The glass forms a special pattern on the road, usually some distance from
where underbody debris falls. When it breaks free, the glass continues to
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December 2009
move and so the point at which it lands can be helpful in determining the
direction of travel of the vehicle from which the glass came and
sometimes the vehicle’s speed. Tempered glass debris areas are,
therefore, quite worth noting and recording. Windshields, which are made
of laminated glass, do not shatter and their after-collision positions usually
mean little.
Solid Cargo. Solid cargo from trucks sometimes comes loose in a collision or
before a collision. The point at which the cargo lands can be important in trying
to find out the direction the truck was moving and something about its speed.
Personal belongings and other cargo in the vehicle as debris rarely signify much
about how the crash happened. They may help understand the nature of the trip
and sometimes help in hit-and-run investigations. Granular cargo spilled as the
result of a collision may be helpful in determining direction of travel and
estimating speed. Roadside material scattered on the road after a collision will
sometimes indicate where a vehicle came back on the road after running off, or
how a collision on the shoulder took place.
Fixed Objects. Bent and broken guardrails, posts, trees, and other fixed objects
can give some ideas of the speed of the vehicle striking them. Insignificant
scrapes and scratches on roadside objects often reveal much about how a crash
happened. Matched with damage or marks on vehicles, they fix the position of
that vehicle at a specific point during the series of events that constitute the
collision. They also help determine the vehicle’s path.
Road Marks
When operators react to an impending crash, their actions may cause tire marks
on the road. Skid marks and scuffmarks have many characteristics in common.
Both occur mainly when heat is produced by the tire rubbing on the road. When
vehicles collide and skid across the road they can cause gouges and scrapes on
the roadway itself. The following are examples of various types of results you
may see at a crash scene:
Skid marks –A skid mark is made by a tire that is sliding without rotation on a
road or other surface. Skid marks look different depending on the type of surface
and its condition. Skid marks made on warm bituminous concrete may show up
as heavy black smears that show some rib marks. The mark is largely
composed of softened and smeared tar or asphalt. On cold, dry cement
pavement, the mark may be a nearly invisible whitish track. Where the material
does not soften with heat, the mark may be composed of rubber that is rubbed or
ground off the tire, which, being tacky from heat, sticks to the road surface.
Normally in crash situations, the driver applies brakes very strongly and very
quickly. This locks the wheels almost instantly and skid marks begin abruptly at
very nearly the same time, with rear wheel marks beginning about the same
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December 2009
place as the front wheel marks. If brakes are not fully applied quickly, each
wheel may lock at a different time, so marks begin at quite different places. This
is especially likely when the car has front wheel discs and rear wheel drum
brakes.
Before the strong and definite mark appears, there may be an indefinite or
questionable area which is sometimes called a “shadow” or “erasure.” In
measuring the skid marks, the clear and distinct part is measured and recorded
as observed. The faint and indistinct additional part, which may be imaginary, is
measured and recorded separately. The distinct and shadow parts of the skid
mark are combined when determining speed from skid marks.
Some examples of skid marks are:
(Braking skid marks)
Because of slower heating, due to a lighter load on them, rear tires may not
begin to make skid marks as soon as the front ones. Rear tire marks usually do
not begin a full wheelbase length beyond front ones. Rear tire marks sometimes
begin further forward than front tire marks and in some instances may be
mistaken for them. Sometimes rear-wheel skid marks are so exactly
superimposed on front-wheel marks that you cannot determine whether the
beginning of the mark was made by a front or rear wheel. When this occurs
simply locate where the mark begins but do not describe it as either front or rear.
Skid marks do not last forever. Certain conditions can affect a skid mark, such
as, the kind of mark, the weather, and the amount of traffic, road repairs or
construction, and sometimes the special characteristics of the tire. Protect tire
marks by keeping people away from them as best you can until you have studied
them.
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December 2009
Skip-Skids. Skip-skids in which the tire mark is repeatedly and usually regularly
interrupted result from three conditions:



Bouncing semi trailers (most common)
Road bumps
Collisions (most significant)
A motor vehicle at point of collision will sometimes cause a shifting of weight from
the front tires to the rear tires for a fraction of a second. When this occurs the
rear wheels will leave a dark or darker mark for a short distance. The rear
wheels may continue to bounce for some distance resulting in a skip-skid.
Collision skip-skids are more likely to occur with small, light vehicles.
Gaps between the marks are usually only a foot or two long. The total length of
the skip-skid should be measured and the measurement recorded. Be sure to
describe the skid as a skip-skid. The length of each skid and gap should also be
measured and recorded.
Gap Skids. In gap skids a set of skid marks ends, there is a gap, and another set
aligned with the first begins. The gap is usually 10 feet or more in length. Gaps
in skid marks are made by release of brake pedal pressure and its reapplication.
Gap skids should be measured in the following manner. For each tire, measure
and record the first skid mark, the length of the gap and then the length of the
second skid mark, etc. This information should be recorded in sequence from
where the gap skid starts and where it ends.
Collision Scrubs. Collision scrubs are not made by braking but by wheels
momentarily kept from rotating by forces of a collision. They help indicate the
point of impact. Collision scrubs are usually no more than 10 feet long and may
present as a skid mark that changes direction abruptly. In same-direction
collisions, they tend to be long and straight. In opposite-direction collisions they
are likely to be short and curved. Sometimes, they are the only mark on the road
that shows the collision point.
After-Collision Skid Marks. After-collision skid marks, made by tires or wheels
which do not rotate for any reason, show the path of that tire precisely. The skid
marks are usually curved after collision because the vehicle is rotating (spinning).
The marks may vary in width from an inch to a foot, depending on how the tire is
aligned in the slide. There may be gaps in after-collision skid marks as the
wrecked vehicle rotates which puts more or less weight on the tire which created
the gap.
Skid marks made by a locked wheel can be determined by looking at the
striations. If the striations (scratches or rib marks) within the mark are parallel to
the mark, the wheel is probably locked. Scuffmarks show the striations oblique
(slanted) to the mark, because the wheel is rotating. The other way to determine
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December 2009
whether the wheel was sliding or rotating is to examine the vehicle to find out
whether the wheel was free to rotate, was locked tight, or could rotate with
enough force to drag it on the road.
Yaw marks – A yaw mark is a scuffmark made on a surface by a rotating tire
which is slipping more or less parallel to its axis. Sometimes yaw marks are
called “critical speed” scuffs, or side slip marks. The difference between skid
marks and yaw marks are that skid marks are made by braking, yaw marks are
made by steering.
Yaw means that a vehicle is rotating about a vertical axis as it moves along a
path. That means that the vehicle is not moving in the direction in which it is
headed. In an ordinary turn, centrifugal force tending to keep the vehicle moving
in a straight line is less than friction force between the tires and pavement. The
rear wheels track inside the front tires. The vehicle follows the path in which it is
steered.
In fast turns, centrifugal force becomes greater than the friction force between
the tires and the road. Tires slip sidewise. The vehicle no longer follows the
path in which it is steered. The rear wheels track outside of the front ones. The
vehicle is no longer headed where it is going but heads more toward the inside of
the curve. During a yaw, the vehicle may veer around enough to slide directly
sidewise and then backwards.
Additional weight on the tires on the outside of the turn produces more friction
heat and makes a stronger mark than the tires on the side of the vehicle toward
the inside of the turn. The tire with the greater weight is not only overdeflected
for that reason, but it is also side deflected to that most of the weight is
concentrated on the outside edge of the tire.
The width of a yaw mark varies from one inch to as much as a foot. Striations in
a yaw mark are not made by ribs in the tread. They are made either by gritty
particles caught in the grooves or by tire sidewall ribs. Any striations that do
appear are nearly crosswise of the mark at the beginning and they change to
oblique (slanted) marks as the yaw progresses. If the mark goes far enough,
striations become parallel to the mark. At this point the wheel momentarily stops
rotating and the tire mark is a skid mark for a short distance.
Yaw marks are always curved because they result from steering. Ordinarily
there are two marks from wheels on the outside of the curve, but on some
material all wheels may show marks. If the yaw continues far enough, the path
of the inside rear wheel crosses the path of the outside front wheel.
Simple measurements of the length of yaw marks are not of much use;
measurements must be sufficient to plot the marks on a map. That means
26
December 2009
locating a point every 10 or 20 feet. When examining yaw marks, look for
striations, and if they are visible, note their direction with respect to the mark.
(Yaw Mark)
Acceleration Scuffs – A scuffmark is made by a tire that is both rotating and
slipping on a road or other surface. An acceleration scuffmark is made when
sufficient power is supplied to the driving wheels to make at least one spin or slip
on the road surface. One way to think about an acceleration scuff is to think
about a race car or a vehicle in the movies that will peel out quickly from a
stopped position. The vehicle may not move immediately because the tires are
spinning with smoke coming out and then suddenly the vehicle shoots off quickly.
This is an extreme example of how acceleration scuff marks are made, but it
gives you a visual of how it happens.
(Creating Acceleration Scuff Marks)
Flat Tire Scuffs – A flat tire mark is a scuffmark made by an overdeflected tire, a
tire which has too little air pressure in it for the load on it. The term overdeflected
means a tire that is over-inflated or under-inflated. If a tire contains a quarter to
three-quarters of its normal air pressure – it will be overdeflected and it will leave
a mark, if any, that is heavy on the edges and light in the middle which looks
much like a front wheel skid mark from a tire overdeflected by weight shift.
27
December 2009
Flat tire marks may extend for many miles along a road. You may not find
exactly where a flat tire scuff really begins because the beginning is so faint.
Completely flat tires have a somewhat different appearance. The tire bunches
up and the sidewalls of the tire also touch the road. The mark made is scalloped
and may show sidewall marks. When one of a pair of dual tires on one wheel
goes quite flat, the other tire on that wheel may then be overloaded and
overdeflected. Both tires can then make marks on the road.
Other tire marks. In loose material such as snow, sand, gravel, mud, or turf, both
skidding and side slipping tires plow furrows. The material is shoved ahead or to
the side, and the bottom is torn up and left rough and irregular. If the pavement
has loose gravel or sand on it, this abrasive material may catch in the tire tread
and leave scratches or grinding marks. This can happen when the road is wet,
but the marks will not show until the road dries off.
Imprints – An imprint is a mark on a road or other surface made without sliding by
a rolling tire. An imprint usually shows the pattern of the tire tread that made it.
An imprint is sometimes called a print, impression, or deposit.
Road Scars – A road scar is any sign that the road, roadside, or a fixed object
has been damaged or marred by a traffic collision. Road scars can be
characterized as scratches and scrapes, towing scratches, gouges, chips, chops,
grooves, grooves made by towing or scars on fixed objects.

Scratches and scrapes are light road scars made by metal and light
pressure on the roadway. The vehicle or object making the scratch
scrapes across the surface of the roadway and leaves a light mark on the
road surface.

Gouges are pavement scars deep enough to be easily felt with the fingers.
Types of gouges are chips, chops, or grooves.

Chips are short, deep gouges; a hole in the pavement made by a strong,
sharp, pointed metal object under great pressure, usually without
striations.
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December 2009

Chops are broad, shallow gouges, even and regular on the deeper side
and terminating in scratches and striations on the opposite, shallower
side; a depression in the pavement made by strong, sharp metal edges
moving sidewise under heavy pressure.

Grooves are long, narrow, pavement gouges; a channel in the pavement
made by a small, strong, metal part being forced in some distance along
the surface while under great pressure.
Falls. When a vehicle falls it is in the air for a short period of time. When a
vehicle runs off a bridge or the top of a bank, it may travel through the air before
it lands. In such a fall, there are no marks between where it left the surface and
where it landed. This distance in the air is the best data for estimating speed
when a car leaves the ground.
Careful observation of skid marks, tire prints or other signs of where the vehicle
left the bank is important, but still more important is examination of the place
where the vehicle first struck the ground again, especially if the vehicle continued
beyond the spot. If necessary, measurements can be made of the slope at the
take-off and the precise vertical and horizontal distances the vehicle moved
through the air.
Flips. Flips occur when the moving vehicle hits something that stops the wheels
suddenly. The vehicle then pivots upward and leaves the ground. Flipping
means that the vehicle flips (rotates) over. The absence of any marks between
take-off and landing is the important fact to establish. The signs of tire marks at
the take-off point must be carefully located so must the signs of landing. Landing
spots will be indicated by torn up turf or snow, crushed brushes, broken ice or
damaged crops. The scar on the roadside where the vehicle landed is usually
irregular and shallow.
Flips follow side slipping or yaw when the tire hits a curb or furrows. For speed
estimation purposes, only the first of a series of flips is important. The take-off
and landing points have to be identified and located as soon after the crash as
possible because they may be obliterated in a short time.
Vaults. Vaults are endwise flips. They occur only when front wheels, sliding or
rolling, are stopped by an obstacle, usually a curb, high enough and vertical so
that the wheel does not roll over it. This means a height equal to three-quarters
as high as the hub or more. Obtain measurements on exactly where the vehicle
lifted off the ground and where it landed, whether it stopped there or not.
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December 2009
Meanings of Marks
It is not important to determine exactly how all of the marks were made at the
crash scene. If needed, the significance can be determined during a follow-up
investigation or reconstruction. In order to determine the significance at a later
date, it is important to locate the marks and describe them well enough so that
such a determination may be made afterward by you or someone else.
Do not infer that because there are no marks left on the road there was no
skidding or scuffing. Especially do not conclude that in the absence of such
marks, there were no evasive tactics such as braking or steering. Vehicles with
antiskid brakes, for instance, do not lock up the wheels and therefore do not skid.
Irregularities in either skid marks or yaw marks are important in determining how
and where a collision occurred when a vehicle collides with another vehicle, a
fixed object, or even a pedestrian or animal, its path is changed in some way,
especially if it is skidding. If tire marks are being made at the time, the change in
path usually shows in tire marks as a crook or a scrub of some kind.
In addition to the results of the collision, other evidence may be significant in a
particular collision. This evidence is frequently temporary in nature, and should
be located during the at-scene investigation. Parked or disabled vehicles may
have contributed to a collision or presented a view obstruction. Positions where
witnesses observed the collision should be located and temporary objects or
conditions which may have contributed to the collision, such as ice patches,
puddles, snow piles, barricades, and excavations should be located.
LOCATING SPOTS FOR EACH RESULT
After determining what evidence to locate, you must decide how many spots are
required to position each object, or identify it accurately in your field sketch and
through measurements. One spot may sufficiently locate small objects, however,
larger objects such as vehicles or long tire marks cannot be adequately located
with just one spot.
One spot will adequately locate relatively small objects such as:



A human body should be measured to the middle of the waist. Severed
bodies will require one spot to locate each part.
Gouges less than three feet long or groups of gouges in an area less than
three feet across can be located by the middle of the group, and
supplement the measurements with photographs and a sketch detailing
the gouges.
Grooves, collision scrubs and tire marks less than three feet in length
could be measured to the middle of the mark.
30
December 2009




Contact damage or damage to fixed objects restricted to a small area less
than three feet across can be located by one spot.
Spatter and puddles less than three feet across.
Small debris areas less than three feet across.
Vehicle parts such as wheels which have become dislodged.
Two spots are necessary to locate objects such as:






Vehicles. At least two spots are required to locate a vehicle. Undamaged
corners along the same side of the vehicle are acceptable. Avoid using
corners along the same end of the vehicle, as they are too close to
accurately locate the vehicle. It is preferable to locate the wheels of the
vehicle in lieu of the corners, particularly if the vehicle is stopped at the
end of tire marks. This will also serve as the point establishing the end of
the tire marks. Measure from the center of the wheel hub.
Straight tire marks. Locate each end of the tire mark.
Curved tire marks greater than three, but less than eight feet in length.
Locate the ends.
Straight grooves greater than three feet in length. Locate both ends.
Contact damage or fixed objects extending over a great length.
Dribble paths.
Three or more spots are required to adequately locate objects such as:



Curved tire marks greater than eight feet in length. Yaw marks (sideslip
scuff marks) can reach great lengths with varying radii. Locate both ends
and intermediate spots where the tire mark crosses a roadway edge, lane
line or centerline. This may leave a long stretch without any spots. If this
occurs, measure additional spots at ten foot intervals. If the mark is
greater than thirty feet in length, ten to twenty foot intervals may suffice.
Also, depending on the degree of the curve, you may need to mark spots
at closer intervals to adequately depict the curve.
Straight marks with angles, such as crooks, gaps, or other irregularities.
Locate both ends of each mark and any angle or irregularity.
Large debris areas. Measure three to six spots along the perimeter of the
area. Include only the substantial deposits of debris.
A tire mark may change to a furrow upon leaving the pavement. Treat it as a
single tire mark, locating both ends, the spot where it crosses the pavement
edge, and any intermediate spots as necessary. Additional spots you should
locate are where a tire mark, especially a curved tire mark, begins or crosses
another tire mark, a roadway edge, a centerline or lane line, or a railroad track.
31
December 2009
MEASUREMENT SYSTEMS
After locating the results and spots, your next step is to decide what
measurement system you will use measure the scene. The goal of measuring at
the scene of collisions is to produce a scale after-collision situation map. Anyone
should be able to take your measurements and draw a scale diagram without
being familiar with the collision scene. If they are not able to do so, the
measurements were not correctly taken. There are three methods you can use
to measure the scene. The three methods are:



The coordinate system using a straight roadway edge as a reference line;
The triangulation system which uses permanent landmarks as reference
points; or
A combination method which uses a combination of the coordinate system
and triangulation system.
The coordinate system works best when you have a lot of straight line roads with
gutters and curbs, such as on a city street, which you can use as reference lines
and reference points. The triangulation method works better for scenes that are
larger, are located at a curve in the road, or are in an area that does not include
well developed roads. For example, you may use this method on a curvy,
country road that has some permanent landmarks nearby, such as a farm house,
water tower, or silo, etc. You can use these landmarks to triangulate the crash
scene better than using the coordinate measuring system.
You may come across a scene where you must use a combination method; using
the two separate systems to measure different parts of the scene. For example,
you may have the main part of the crash scene located on a road that allows you
to use the coordination method. However, you may have some sort of debris
that flew quite a distance from the main crash site. You may find it easier to use
the triangulation method to measure the debris that flew away from the main
crash area. In this case, you use both systems to measure and document this
crash scene.
Coordinate System
In Figure 3-1, there are three spots to be measured; you could use the two
corners of the car if there is no damage on one side, or the preferred method,
using the center of the wheel hubs, C1 and C2; and a body, B. Many officers will
also measure the distance between the car and body. For example, it may be
ten feet between the body and the end of the car. That locates neither the car,
nor the body. Both can be anywhere on the map, as long as there is ten feet
between them. However, if you describe point B as lying thirteen feet north of
the south curb of Oak Street, and 46 feet east of the back of the sidewalk along
the east side of Elm Street, there is only one spot where the body can be located.
32
December 2009
LAMP POST
OAK ST.
B
RL = S EDGE OAK
RP @ E EDGE E SIDEWALK ELM
C
IMAGINARY EXTENSIONS
C1
N 13.0
C2
RP
E 46.0
RL
SIDEWALK
0
ELM ST.
10
20
FEET
Baker, K. S. (2001) Traffic Collision Investigation, p. 190
(Figure 3-1)
The coordinate method requires two measurements, or coordinates, to locate
each spot. These measurements must be made from two permanent, easily
identifiable landmarks. Anyone returning to the collision site should be able to
reestablish these landmarks. You must select your landmarks before starting to
measure.
In the coordinate method, one landmark is referred to as a reference line (RL),
and the other as a reference point (RP). The reference point, sometimes called a
zero point or starting point, establishes the origin (center) of your coordinates.
The reference line is a line, either real or imaginary, which extends through or
alongside the collision scene from which measurements can be made. The
reference point must be a point on the reference line, or a point opposite a
landmark near the reference line.
The reference line can either be a real or “natural” line such as the edge of the
pavement. A natural reference line provides a visible, permanent line from which
to measure. Such reference lines are easily described, and are seldom confused
by others. However, the results of many collisions lie within an intersection
where no natural reference line exists. In such instances, it may be possible to
establish an imaginary reference line. The imaginary extensions of the roadway
edges are most commonly used for this purpose.
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December 2009
In addition to the two measurements required in the coordinate method, a
direction of each measurement is needed. The directions, N, S, E, and W, are
used for this purpose. Compass directions may be used; however, the more
widely used method is to use nominal directions instead. The nominal direction
is the general direction of the roadway. If you choose to use the “true” or
compass direction, you should label your field sketch as such. You must record
the direction of the spot to be located from the reference line to a point opposite
the spot to be located.
When describing the reference lines, especially roadway edges, it should be
clear which line was used. There may be several suitable reference lines along
the edge of some roadways. A roadway bordered by a concrete curb and gutter
with a painted edge line presents several options. If the curb is used as a
reference line, the investigator should specify to which edge the measurements
were taken. The vertical edge of the curb facing the roadway is referred to as the
“face” of the curb. The edge of the curb which is adjacent to the roadside is
called the “back” of the curb. Either edge is a suitable reference line for
unmountable curbs; however it is usually easier to measure to the face of the
curb. The back of the curb is the preferred reference line for roadways bordered
by a mountable curb as the face is not readily discernable.
In the absence of a curb, the edge of the pavement is typically used as a
reference line. Many investigators have used the painted edge line as a
reference. These lines are typically four to six inches in width, and periodically
repainted. The edge of the pavement provides a more precise and permanent
reference from which to measure. When using these painted edge lines,
measure to the middle of the width of the line. Irregular pavement edges require
that the investigator use what seems to be an average or “best fit” as a reference
line.
Triangulation System
The triangulation method also requires that two measurements are made to each
spot. When using triangulation, these measurements are from two reference
points. A triangle is then formed by the spot to be measured and the two
reference points. The measured spot is located at the intersection of the
distances to each reference point. The distance between the reference points
creates a triangle of which the lengths of all three sides are known.
Triangulation is useful in situations when it is not convenient to use the
coordinate method. These situations include:


Roadway edges are indistinct or obscured, making them difficult to be
used as a reference line.
Spots to be located are more than 30 feet off the roadway. The
coordinate method requires that investigators sight a right angle between
34
December 2009


the spot to be measured and the reference line. It becomes difficult to
accurately estimate the right angle when the distance from the reference
line to the point is more than 30 feet.
Roadway edges are irregular or complicated, making them difficult to be
used as a reference line.
Spots are located off the road where no natural reference line exists.
LAMP POST
RP2
35
4
RP1 = HYDRANT S OF OAK
RP2 = LAMP POST N OF OAK
2
28 FROM RP1
B
23 0
28
OAK ST.
2
C
C1
C2
RP1
1
31
4
0
HYDRANT
SIDEWALK
0
ELM ST.
10
20
FEET
Baker, K. S. (2001) Traffic Collision Investigation, p. 199
(Figure 3-2)
Locating spots by triangulation requires measuring the distance to a spot from
two reference points, RP1 and RP2. To relate the reference points to the
roadway, supplemental measurements are needed: The distance between the
reference points, and the shortest distance from each reference point to the
roadway edge. Reference points do not need to be on opposite sides of the
roadway.
In figure 3-2, the reference points are described as RP1 = Hydrant S of Oak and
RP2 = Lamp Post N of Oak; 282 from RP1. The distance to spot B is measured
from both reference points. Spot B is 311 from RP1 and 354 from RP2. These
distances form two sides of a triangle. The third side is formed by the distance
between the reference points. It is 282 between RP1 and RP2. The location of
spot B can be established by drawing a triangle with sides equal to the measured
distances.
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December 2009
The right angle (shortest) distance from each reference point to the pavement
edges is needed to draw the reference point relative to the roadway. In figure 32, RP1 is 40 south of the south edge of Oak and RP2 is 230 north of the south
edge of Oak. Measure these distances to the same edge of the roadway.
Triangulation is similar to the coordinate method in that it requires two
measurements per spot. In fact, any method requires at least two measurements
to locate a spot. Triangulation differs from the coordinate method in three ways:



No reference line is used.
The two measurements are not necessarily at a right angle to each other.
There is no need to specify the direction of each measurement.
Many of the same factors considered when using coordinate measuring
techniques apply when selecting reference points for use in triangulation.



Safety. Select reference points which keep investigators out of traffic, and
do not expose them to unnecessary hazards.
Proximity. Measurements are typically longer when using triangulation. If
possible, select reference points which do not require measuring
distances greater than the length of your tape. A 200 ft roll-up tape is
particularly useful in triangulation.
Identification. Use easily identifiable and describable reference points.
Anyone returning to the collision site should be able to reestablish your
reference points.
Combination of Systems
The coordinate method is the preferred method of measuring at a crash scene.
Triangulation provides a means of taking measurements when the coordinate
method fails, or is not convenient. By no means are you restricted to using one
method only at the scene of a collision. Circumstances may occur when both
coordinates and triangulation are used at the scene of a collision. In these cases
you may need to create a separate table for each set of measurements on your
field sketch.
36
December 2009
MARKING SPOTS ON THE ROAD AND ROADSIDE
Marking Supplies
Sometimes you will need to mark roadway evidence, reference points, and other
spots of interest. Spray paint is an effective way to mark spots on dry, hard
surfaces such as the roadway. Bright orange works best for marking crash
scenes. Crayons or chalk can be used to mark concrete or asphalt. Lumber
crayons work well for this purpose. They are sold in various colors; however,
yellow is the most common. Crayon marks are not as permanent as paint;
however, they perform better on wet surfaces.
A small supply of nails will work well to mark spots along the roadside (in
surfaces such as grass, dirt, etc.). To increase their visibility, tie a piece of
flagging or attach an index card to the nail. Evidence cards are an effective
means of marking the location of small evidence in photographs. Homemade
cards or small orange cones used to mark athletic fields can also be used to
identify evidence.
Marking Spots
After determining which measurements system you will use, mark spots on the
road and roadside to help when taking measurements. Assign a letter to each
item to be located. Try to use letters which are descriptive of the item they
represent. For example, a truck may be labeled T, and a car in the same crash
may be labeled C. The letter F may designate a Ford, and a C may designate a
Chevrolet. Other letters that may be used to indicate other items include letters
such as D for debris, G for gouge, or B for body. If there is no logical letter to
represent an item, or it has already been used, any letter will suffice. However,
avoid using vehicle or unit numbers that appear on the crash report.
Use numbers to denote multiple spots for the same object when more than one
spot is necessary to locate an item. For example, the letter D may be used to
identify a debris area, with points along the perimeter designated D1, D2, D3,
etc. Long curved tire marks can also be labeled in this manner.
Figure 3-3 shows examples of how letters with numbers denote multiple spots for
the same object.
37
December 2009
S1
10 Foot
Intervals
C
C1
C2
S2
S3
D1
S4
D2
S5
D3
S6
(Figure 3-3)
You should mark the following spots:


Reference points when using coordinate measurements. Often your
reference point is opposite a definable feature such as a utility pole or fire
hydrant, at the imaginary extension of two roadway edges, or at the
beginning of a curve.
Final rest position of bodies. Often pedestrians and ejected occupants are
removed for medical treatment. Their final rest positions are crucial
evidence in an investigation. Reestablish and mark their position(s).

The positions of two or more wheels of involved vehicles. Undamaged
wheels are preferable. Ensure that if only two wheels are marked, they
are from the same side of the vehicle. This will enable removal of the
vehicles before measurements are completed. Other vehicles which
should be marked are parked vehicles which are suspected of creating a
view obstruction.

The ends of tire marks. The beginning of tire marks is not always easily
seen. These marks may be more visible when viewed from different
38
December 2009
directions or angles. Marking the beginning of the tire mark will make it
easier to measure.

The end of your tape. It may be necessary to measure a distance greater
than the length of your tape. Mark the end of the tape, and move ahead.
Write the distance to the point in crayon or paint.

Stations along the reference line. When measuring long curved tire
marks, it is necessary to measure to points at 10 to 20 foot intervals along
the reference line. Marking these intervals (stations) along the reference
line makes taking these measurements easier and faster.

Significant evidence. The maze of tire marks, metal scars, and debris can
be more easily deciphered if marked. Descriptions used on the field
sketch can also be marked adjacent to the corresponding evidence. This
will make measuring easier and quicker. Caution: Do not mark the
scene if you are calling in a specialist or reconstructionist.
Circumstances will dictate whether marking the scene is necessary, and when it
should take place. Whenever possible, try to take all the essential photographs
before marking the scene. Photographs depict the condition of the scene
following the crash. Additional photographs can be taken after marking the
scene. The use of bright paint will increase the visibility of evidence in
photographs. Marking the position of small evidence with evidence cards will
also improve their visibility in photographs.
CRASH SCENE DIAGRAMS AND SKETCHES
Field Sketch
An at-scene investigation should include a field sketch. The field sketch provides
a pictorial supplement to the at-scene measurements. It depicts the relative
positions of the results of the crash and eliminates the need for lengthy
descriptions.
The field sketch should include the results of the collision, roadway features, and
significant objects which may have contributed to the collision. It is limited to
factual data, and the investigator should not list opinions. Evidence such as
collision scrubs, crooks, or metal scars should be clearly labeled. These may be
indications of the point of impact. However, the point of impact is an opinion and
should not be labeled on the field sketch.
The field sketch is a not-to-scale, free hand drawing. It is intended to supplement
field measurements. Often the table of measurements can be included on the
39
December 2009
field sketch. Letters used to identify points in the table of measurements can be
indicated on the field sketch next to the corresponding points.
The field sketch should be drawn while at the crash scene. It should fit on letter
sized paper. Graph paper works well for this task. Do not crowd too much
information on the sketch. Use additional paper if necessary, and consider
placing the table of measurements on a separate sheet.
Roadway Skeleton
Begin the field sketch by placing a north arrow in an out-of-the-way corner of the
field sketch. It is preferable to orient north toward the top of the sketch.
However, since your paper is rectangular, there are instances when you may
prefer to orient north toward the left or right edges. On roadways which do not
run due north-south or east-west, the north arrow should indicate nominal north
(the direction generally considered to be north).
Continue by drawing the roadway edges. This “skeleton” (Figure 3-4) will include
only the pavement edges. Shoulders and returns (small radius curves which
connect intersecting roadway edges) do not need to be drawn unless significant.
Oblique roadway angles should be approximated, and large radius curves can be
drawn straight. Show the alignment of the roadway edges as they are at the
scene. Draw a dashed line through intersections to indicate aligned edges.
Difference in roadway widths, and offset intersections should be depicted. Be
sure to leave sufficient room to draw the results of the collision.
N
Baker, K. S. (2001) Traffic Collision Investigation, p. 218
(Figure 3-4)
40
December 2009
Identification
The field sketch should include the time, date, and location of the collision. The
name of the person preparing the sketch, and persons assisting with
measurements should also be included. If the measurements are not taken at
the time of the collision, list the date and time the measurements were taken if
done at a later time.
The location data should include the name of the street, road, or highway on
which the crash occurred, the intersecting street, or distance from a definable
intersection, and the city, or county and state in which the crash occurred. Many
agencies assign a report, incident, or dispatch number to each collision or
incident. This number should also be included on the diagram to further identify
it. (Figure 3-5)
COLLEGE
N
NORTH ST
RIPON, WI
JUNE 13, 2007. 3:45 PM
SKETCH BY D. DORN
ASSISTED BY D. KNAPP
BIRT
REPORT NO. 07-321
Baker, K. S. (2001) Traffic Collision Investigation, p. 218
(Figure 3-5)
Results of the Collision
After drawing a roadway skeleton, begin adding the results of the collision. Show
final rest positions of the vehicles, pedestrians, and ejected occupants. Use a
rectangle to indicate positions of vehicles. Specify the front of each vehicle with
a triangle or an arrow. Draw diagonal lines from each corner of the rectangle to
indicate an overturned vehicle. Stick figures are adequate to indicate positions of
41
December 2009
bodies. Show the approximate orientation of the body’s head and feet on the
sketch.
Show tire marks on the field sketch. This should include not only pre-impact skid
marks, but also post impact tire marks, yaw marks, and tire prints. Pay close
attention to crossover points and try to approximate radii of curved tire marks.
Indicate the approximate direction of striations in yaw marks and scuff marks by
hash marks drawn across the tire mark. (Figure 3-6)
No Cross Striations
With Cross Striations
Baker, K. S. (2001) Traffic Collision Investigation, p. 218
(Figure 3-6)
Add metal scars, debris, spatter, dribble, run-off and soak-in. Metal scars often
appear in small clusters which may be difficult to fit on the field sketch. Consider
creating a detailed sketch of this area with a separate table of measurements.
Include the length, width, and depth of each scar in this table. A single point in
the center of the cluster should be measured by coordinates or triangulation.
Include any fixed objects struck during the collision and indicate the area of
contact to these objects on the field sketch. Show the location of any objects
which may have contributed to the collision such as view obstructions. Their
positions should be measured. In the case of parked vehicles, be sure to include
the vehicle description on the field sketch. A Mazda Miata does not provide the
same view obstruction as a Ford Excursion. Draw the position of any unusual
circumstance such as construction zones (barricades, cones, etc.) and pavement
irregularities (potholes, roadway debris, friction zones, etc.).
42
December 2009
Labeling
The features depicted on the field sketch must be labeled. Space constraints
necessitate the use of abbreviations and alpha-numeric labels. More lengthy
descriptions can be included on the table of measurements to prevent the field
sketch from becoming too cluttered.
Choose logical letter descriptors for your field sketch. For example, the letter D
may be used to label a debris field and G for a cluster of gouges. Use care not to
duplicate any descriptors.
Begin labeling the roadway on which the crash occurred and any intersecting
roadway(s) or drives. You may find it difficult to orient all text in one direction. It
is okay to write some text vertically, but it is preferred to orient all text so it can be
read from the bottom or right side of the paper. Avoid writing upside down or
from the left side of the paper.
Label your reference line and reference point(s). Use the label “RL” for a
reference line and “RP” for reference point(s) on the sketch. A complete
description of each should appear either on the table of measurements or in a
less cluttered area of the field sketch as shown below.
Rhinelander, Wisconsin
2:05 PM. NOV 25, 2007
SKETCH BY M. DRAPKIN
REPORT NO. 501-059
Point
CTH C
N-S
E-W
TRUCK
T1
T2
N24.0
N20.0
W9.7
W29.3
CAR
C1
C2
N47.7
N53.3
E12.2
E28.9
FURROWS A1
A2
B1
N70.0
N61.2
N56.3
E5.0
E15.0
E10.5
N
A1
2
A
B
1
C1
C2
C
T1
T2
RL = E EDGE CTH C
RP = OP DO NOT PASS SIGN
MOEN LAKE ROAD 1.5 MILES
T
RP
DO
NOT
PASS
RL
Baker, K. S. (2001) Traffic Collision Investigation, p. 220
(Figure 3-7)
Label the rest position of each vehicle. A letter descriptor is adequate for the
field sketch and a more complete description can be included in the table of
43
December 2009
measurements. Indicate the points on the vehicle to which measurements were
made. Use a numeric suffix to identify individual points. For example, in the
sketch above, T1 indicates the left front wheel of the truck and T2 indicates the
left rear wheel.
Give each tire mark a separate letter descriptor. Use numeric suffixes to identify
multiple points on the same tire mark. A more complete description of each tire
mark should be included in the table of measurements. Label multiple points
around the perimeter of large debris fields. Small debris areas may require only
one point. Clusters of metal scars require a single point to be labeled. However,
long scratches or grooves may have to be labeled in the same manner as a tire
mark. Consider labeling multiple points around the perimeter of large scrapes
when necessary.
Roadway dimensions such as road and lane widths can be labeled on the field
sketch. Offsets at intersections and curve radii can also be dimensioned on the
field sketch. Use care though and do not clutter the field sketch. If necessary,
include these dimensions on a separate field sketch depicting only the roadway
features. The field sketch may also include the type of pavement (asphalt,
concrete, etc.) and surface condition (wet, dry, etc.).
44
December 2009
ROAD FEATURES
SIGNIFICANT ROADSIDE OBJECTS
ROADWAY EDGE
WITHOUT CURB
X
X
X
v
v v
v
X
X
FENCE
STEEP BANK (Points
Downhill)
CURB
v
v
v
v
DITCH
v v
v v
v
v
SHOULDER EDGE
v
SINGLE GUARD RAIL
STREAM, POND, LAKE
DOUBLE GURAD RAIL
UTILITY POLE
.
.
MASONRY SEPARATOR,
BRIDGERAIL, PIER
CORRUGATED
RUMBLE MEDIAN
TREE,
UNOBSTRUCTED VIEW
SHRUBBERY, TREE
(OBSTRUCED VIEW)
LAMP POST, HYDRANT
RAILROAD TRACKS
. . . . . . . . .
CROPS
(OBSTRUCTED VIEW
v v v
v v v v
PROPERTY LINE
UNMARKED CENTER
BUILDINGS
MANHOLE, INLET, DRAIN
ROAD USERS
SIGNS OF CRASH ON ROAD
PERSON UP
AND DOWN
SKIDMARK
YAWMARK
CYCLE UP AND
DOWN
OTHER TIRE MARKS
VEHICLE UPRIGHT
AND OVERTURNED
TIRE SCRUB
FURROS
... ... . ... . .
... ... . ... . .
TRUCK
BUS
SPATTER & DRIBBLE
PUDDLE & RUNOFF
TRACTOR AND
SEMITRAILER
OTHER DEBRIS
GOUGES
PARKED VEHICLE
SCRATCHES, SCRAPES
TRAFFIC CONTROL DEVICES
ADDITIONAL USEFUL SYMBOLS
BROKEN LANE LINE
NORTH ARROW
0
BARRIER LINE
10
FEET
20
SCALE
LANE REFLECTORS
-0.02
STOP
50
MPH
TRAFFIC SIGN
GRADE (FT/FT)
+ IS UPHILL
SIGHT LINE
RED
FLASHING SIGNAL
CAMERA POSITION
TRAFFIC SIGNAL
Baker, K.S. (2001) Traffic Collision Investigation, p. 245
(Figure 3-8 Recommended symbols for use on field sketches.)
45
December 2009
RECORDING BASIC MEASUREMENTS
Table of Measurements
You will need to record numerous measurements at the crash scene. To avoid
cluttering the field sketch, create a table of measurements. This table can
appear on the field sketch or you can place it on a separate sheet to supplement
the field sketch. The table organizes the information and helps ensure that no
measurements are omitted.
First, decide if the table of measurements will fit on the field sketch. If there is
any doubt, place it on a separate sheet of paper. When using a separate sheet,
repeat the reference point(s) and reference line descriptions and crash
identification information on the table.
Next determine whether coordinate measurements or triangulation will be used to
measure the scene. In some cases more than one method will be used. It may
be necessary to use two reference lines or use both coordinate measurements
and triangulation. A separate table of measurements is needed for each set of
measurements.
The table should be divided into columns. Label the first column “Spot” or “Spot
Description.” It should include the corresponding alpha-numeric descriptor used
on the field sketch. This column may be used to provide additional spot
descriptions such as skid marks, debris, gouges, etc. The second and third
columns are used for measurements.
For coordinate measurements, the second column will be used to record north
and south measurements and the third column will be for east and west
measurements. Label each column as “N-S” and “E-W” respectively.
Remember to use nominal directions as previously described. For triangulation,
the second column will be used to record the distance to reference point 1
(labeled RP1) and the third column will be used to record the distance to
reference point 2 (labeled RP2). (Figure 3-9)
46
December 2009
Coordinate Method Table
POINT
N-S
Triangulation Method Table
E-W
POINT
RP1
FORD
F1
F2
SATURN
S1
S2
DODGE
D1
D2
PONTIAC
P1
P2
SKIDMARKS A1
A2
A3
SKIDMARKS A1
A2
GOUGE
G
RL = E EDGE WELSHIRE
RP@N EDGE SPRUCE HILL DR
RP1 = UTILITY POLE 5406
RP2 = HYDRANT SE CORNER
RP2
Baker, K. S. (2001) Traffic Collision Investigation, p. 221
(Figure 3-9)
The field sketch should include only factual data. It is a record of your
observations while at the scene. No opinion or conclusions should be depicted.
Things that should not be listed on a field sketch include:

The point of impact (or POI) is an opinion, not an observation and should
not be listed on the field sketch.

The paths traveled by the vehicles before and after the collision should not
be depicted on the field sketch. These paths are also an opinion and not
an observed fact. Tire marks should be listed, but do not list the direction
of travel on the sketch.
There are data recorders (handheld instruments) that record data at a crash site
and can then be downloaded into a computer. Computer software then uses this
data to create a drawing after the survey. However, this does not eliminate the
need for a field sketch. Complete a field sketch to aid the instrument operator in
assigning description codes to various features.
MEASURING
The basic equipment needed for scene measurements is minimal. To help
prepare the field sketch you need a clipboard, paper, and a writing instrument.
Grid paper will make it easier to draw a field sketch and maintain proper
alignment of features depicted. The grid will also help create the table of
measurements. The writing utensil should be a good mechanical pencil (have
47
December 2009
extra lead available). You will also find the need to erase items from your notes.
A good plastic eraser works better than the traditional red rubber eraser. The
inability to erase and poor performance in wet and cold conditions make ink pens
impractical.
A micro-cassette recorder is an invaluable piece of equipment. Observations can
be easily and rapidly recorded at the scene of the collision and transcribed later.
The recorder performs well in the rain and snow, but may not work well in
extreme cold. However, using a recorder to take measurements should not be
done except by experienced investigators. It is better to write down the
measurements while still at the scene of the collision. If you record these
measurements verbally versus writing them down, you run the risk of omitting
needed measurements. A micro-cassette recorder is also useful for recording
witness and driver interviews, but be sure you follow the proper procedures for
taping these interviews according to your department policy.
Measuring Devices
A variety of measuring devices are available. The bare minimum should include
a 100 foot roll-up tape and a 25 foot tape measure. Fiberglass roll-up tapes are
usually available in 100 foot and 200 foot lengths. A 100 foot tape is usually
sufficient. The roll-up tape works well with both the coordinate and triangulation
measurement methods. When using the coordinate method, string the tape
along the reference line with the zero-end at your reference point. If the surface
is flat, and it is not too windy, a pin, a nail, or weight can be used to hold it in
place. Distances along the reference line can easily be read from the tape. The
tape can also be used as the reference line when extending roadway edges or
measuring along curves.
When using the triangulation method, the distance from each reference point to
the point to be measured frequently exceeds 25 or 50 feet. Try to select
reference points within 100 feet of the points to be measured. If this is
unavoidable, use a 200 foot roll-up tape if you have one on hand.
A spring loaded pocket tape measure is useful for measuring short distances.
They are available in lengths from 3 to 30 feet. The longer the tape the more
useful it will be, however. Tape measures are most useful when using the
coordinate method of measuring. To ensure that a right angle measurement
from the point to be measured to the reference line is obtained, the distance
should be kept less than 30 feet. Tape measures are also invaluable for
documenting vehicle dimensions and damage measurements.
Measuring wheels are ideal for long measurements over clean, smooth surfaces.
Measurements can be made by one person and more quickly than with tape.
However, these wheels follow the terrain which makes them useless for
measuring over uneven surfaces such as ditches. Measuring wheels do not
48
December 2009
work well on snow or ice either because they depend on friction to turn the
wheel. As a whole, they are not as accurate as tape and they should be
considered as a supplemental piece of equipment and should not be used in lieu
of a measuring tape.
Using Measuring Tapes
Short distances are easily measured with the tape measure. Under most
conditions, it can be operated by one person with one hand. The end of the tape
measure can be hooked on edges or butted up against a vertical surface. It is
well suited for measuring:






Vehicle dimensions. The length, width, wheelbase, track width, and
overhangs are typically less than the length of the tape measure. The
preferred units for vehicle dimensions are in inches.
Height and sizes of signs.
Height of curbs, roadway drop-offs or lips, and depth of potholes.
Width of sidewalks, or other improvements.
Lengths and widths of metal scars.
Distance of points to the reference line in the coordinate method.
For distances over ten feet, it becomes difficult for one person to use the tape
measure. Have an assistant help you take measurements. Anyone capable of
holding the end of the tape can help, but if you can find someone with experience
the process will not require you to give much guidance.
If both investigators are experienced, either can record the measurements. It is
usually quicker if the investigator recording the measurements holds the zeroend of the tape. This frees him/her to write down the distance while the assistant
handles rolling up or retracting the tape and moving to the next point. It is
imperative that the measurement is recorded accurately. The investigator
recording the measurement should repeat the distance to the assistant for
verification.
Roll-up tapes are used for longer distances. When using the coordinate method,
extend the roll-up tape along the reference line. If possible, use a chaining pin,
nail, or weight to secure the zero-end of the tape at the reference point. The tape
should be sufficiently secure to permit the tape to be pulled taut during
measurements. An assistant may be required to facilitate this. The roll-up tape
works well measuring distances along the reference line to the reference point.
If your reference line is the extension of a roadway edge, the roll-up tape can be
used to provide a line to which to measure. Line up the tape with the roadway
edge and extend it into the intersection. When possible, extend the tape to meet
the aligned edge on the opposite side of the intersection. This will eliminate any
errors in sighting the roadway extensions.
49
December 2009
When measuring a curved roadway with a large radius as a reference line, a rollup tape can provide a straight line to which to measure. It is not possible to
measure along a curve with a tape. Instead, extend the tape across the curve.
The zero-end of the tape should be at the reference point.
Triangulation usually involves distances over 25 feet to one or both reference
points. For this reason, the roll-up tape is better suited for this method. It is
usually quicker to measure to all points from one reference point, then switch to a
second. Care must be taken to measure the identical point from each reference
point, ensuring that no measurements are omitted.
Distances should be measured horizontally, or level. Small roadway grades do
not introduce large errors in short distances. However, when measuring over
uneven surfaces such as ditches, the tape must be pulled taut and kept level.
Measure to the center of poles, fence posts, trees, fire hydrants, and circular or
rectangular objects on or adjacent to the roadway such as manholes, and inlets.
This is the conventional practice, and well be assumed by others unless
otherwise specified.
When locating final rest positions for vehicles, measure to the center of the
wheels or corner (acceptable but indicate this clearly). Measurements to
undamaged areas are preferred, but nothing prevents you from measuring to all
four wheels or corners. Measure directly to the outboard edge of the tire directly
below the axle or to the corners. It is often easier to measure the final rest
position after the vehicle has been removed. Ensure that its location is properly
marked and that your marks will not be obliterated during the vehicle’s removal.
It is common to measure to the center of tire marks. If for any reason this
practice is not followed, be sure to indicate on the field sketch the exact point to
which the measurement was made.
Reading Tapes and Recording Measurements
Measuring devices using imperial units are graduated in feet and tenths, or feet
and inches (twelfths). Both units may be printed on one tape. Feet and tenths
are used by engineers and surveyors and are the preferred units for measuring
at crash scenes. Inches are the preferred units for vehicle dimensions and
damage measurements. Check your tapes to determine which units are on
them. If your tape(s) contain both, decide which units you will use and ensure
that anyone assisting you is aware of this.
When using units of feet and tenths, simply record the distance with a decimal
point between. For example, the distance of 2 feet and 7 tenths should be
written as 2.7. For distances less than 1 foot, it is common practice to write a
zero before the decimal point. For example, the distance of 6 tenths would be
50
December 2009
written 0.6. The zero before the decimal point reduces the possibility of
confusing this distance with six feet.
The method of writing feet and inches varies from one discipline to the next. A
usual way to indicate feet and inches is to use the prime (‘) for feet and the
double prime (“) for inches. However, the prime symbol can be confused with the
number 1. For this reason, this method is not used in crash investigations. If
inches must be used, indicate that by superscripting and underlining the inches.
For example, six feet, 5 inches would be written, 65. When recording distances
less than one inch, include a zero before the distance as in 0 8 to eliminate
confusion. Some tape measures are graduated in inches only. Follow the same
convention of including a zero before the distance. For example, the distance 78
inches would be written 078.
Accuracy (how close a measurement is to the actual distance) is important in
crash investigations. Measurements should be made to the nearest tenth of a
foot. To indicate that a distance was measured to the nearest tenth, record the
first digit to the left of the decimal point, even if it is a zero. The distance 5 feet
should be recorded as 5.0.
Errors in accuracy usually result from carelessness. Common errors in
measuring are:







Reading numbers upside-down, for example mistaking a 9 for a 6.
Misreading the foot mark, such as reading 15.6 as 14.6 or 16.6.
Confusing the location of zero on your tape. (Not all tapes are imprinted
with a zero at the free end.)
Losing count of the number of complete tape lengths measured.
Forgetting to reset the counter on a measuring wheel.
Attempting to remember distances rather than recording them
immediately.
Adding separate distances mentally rather than recording each
measurement separately and adding them later.
Electronic Measuring Devices
An electronic distance meter (EDM) uses light to measure the distance between
the instrument and the point to be measured. This requires a line of sight
between the instrument and the point. The light beam, or signal, is reflected
back to the instrument. This can be accomplished by two methods.
The first type of instrument uses a reflective target. The target is sighted by a
telescope mounted to the EDM. This type of instrument is extremely accurate
and the range varies by instrument, but 1000 feet per prism is typical. The more
likely method uses reflectivity of an object to return the signal to the instrument.
Laser speed measuring devices used in traffic enforcement are also capable of
51
December 2009
measuring distances. This works well when shooting distances to vertical
surfaces, but becomes difficult to measure to points lying on a horizontal plane.
A vertical target held over the point will make measuring these points easier.
Electronic distance meters are most useful when using triangulation. The
instrument is held over the point to be measured and the distance to each
reference point measured. Coordinate measurements can be performed,
however, with more difficulty. Before you use either of these methods, you must
attend additional training to learn how to operate and properly take
measurements with the equipment.
ADDITIONAL AND SUPPLEMENTAL MEASUREMENTS
Review your field sketch and table of measurements. Ensure all of the basic
measurements are complete. In some cases you may need to take additional
measurements to identify evidence not covered in the basic measurements. You
may also want to include a detailed sketch of evidence, such as metal scars on
the road, which should include supplemental measurements. These
supplemental measurements include length, width, and depth of the scars.
Create the detailed sketch on a separate sheet of paper than the field sketch.
3
1
2
4
5
INCHES
6
L
1
2
3
4
5
6
7
GROOVE
SCRATCH
SCRATCH
SCRAPE
GROOVE
SCRATCH
CHOP
6
11
15
5
7
4
10
W
½
½
¼
1
¾
1/8
1-1/2
D
1/16
0
0
0
¼
0
1/8
7
Baker, K. S. (2001) Traffic Collision Investigation, p. 219
(Figure 3-9 Detailed sketch with supplemental measurements)
52
December 2009
LABELING AND REVIEWING THE FIELD SKETCH
The features depicted on the field sketch must be labeled. Only printed text
should be used (no cursive). Lettering templates and lettering guides are
available but hand lettering is acceptable. The text should be oriented so that it
can be read from the bottom of the page. There may be instances where it is
more convenient to orient text so that it can be read from the right edge of the
paper, however.
As stated earlier, identifications should include the name of the roadway on
which the crash occurred, the intersecting street or distance from a definable
intersection, the city (or county) and state where the collision occurred, and the
time and date of the collision. Additionally, the name of the investigator
preparing the sketch should be listed along with the report or reference number.
Each road, street or highway must be labeled. Include secondary names or
route numbers to identify the roadway. It may be necessary to identify direction
of travel on divided or controlled access highways. Identify railroads, rivers and
creeks or streams. Label any buildings depicted on the sketch. Residences can
be identified by address and businesses by name.
Avoid labeling ejected occupants as driver and passenger because this is an
opinion, not fact. Label signs by type or message. Often the face of the sign is
drawn with an arrow pointing to its location. Other significant features should be
labeled as desired. Try to position labels so that the diagram does not become
cluttered. When needed, draw arrows from the label to the location of the feature
described. The arrow should be drawn from the beginning or end of the label,
never the middle and arrows should never cross each other.
Ensure that north is labeled on your sketch. This is typically indicated with a
north arrow. North arrows are drawn in many styles. The only requisite is that it
clearly shows which way is north. It is not necessary to label the three remaining
directions.
AFTER-COLLISION SITUATION MAPS (SCALE DIAGRAM)
An after-collision situation map is a scale diagram of the results of the collision
and roadway. Scale diagrams are not created for every collision you investigate.
If no legal action arises from a collision, and no reconstruction is performed, a
scale diagram is seldom needed. However, if a trial resulting from a collision is
convened, a scale diagram is usually prepared as an exhibit. Additionally, scale
diagrams are nearly always needed in crash reconstruction.
53
December 2009
Like the field sketch, the scale diagram should only contain factual data.
Opinions or the findings of a reconstruction can be included on overlays or on a
separate diagram. Tire marks, metal scars, and final rest positions of vehicles
and bodies should be depicted on the diagram. Significant features such as
parked vehicles, construction areas, and view obstructions should also be
included and roadway and roadside improvements such as pavement edges,
lane markings, traffic signs and signals, fixed objects, and sidewalks should be
depicted. An after-collision situation map is more detailed and accurately drawn
to scale than a field sketch.
After-collision situation maps are intended to be “true and accurate
representation” of the collision site. If your measurements are wrong or if there
are errors in reading or recording distances, the scale diagram will be inaccurate.
Omitted measurements can also affect accuracy. It is extremely important to
ensure accuracy on your field sketch and in taking measurements to help create
an accurate scale diagram.
Typically, inadequate or missing data is the root of most problems. In many
cases, no measurements were taken at the scene. The results quickly disappear
and can only be reestablished through photographs when available. In some
cases, poor measuring techniques were employed. Reference points are used
which cannot be reestablished or the investigator may fail to follow any method
for taking measurements. A typical error results when single measurements are
made to one reference point. It is impossible to locate any point with only this
data.
Templates
Traffic crash templates are instruments that allow traffic crash investigators,
engineers, architects, claim adjusters, lawyers, and other professionals to quickly
prepare scale maps of traffic crashes, calculate speeds from skidding distances,
estimate stopping and acceleration distances, change miles-per-hour to feet-persecond (metric model changes kilometers-per-hour to meters-per-second),
measure angles and grades, and illustrate arrangement of parked vehicles. Made
of transparent plastic, it also serves as a clinometer to measure road grades and
super elevations when used with a slightly modified clipboard. Examples of two
templates are shown in Figures 3-10 and 3-11.
54
December 2009
(Figure 3-10 Traffic Crash Template)
(Figure 3-11 Mini-Template)
Return the Scene to Normal (Normalize)
When responding to a crash scene, the first steps you take are protecting life and
preserving evidence. You may have to divert traffic around the crash scene in
nearby lanes or you may have to detour drivers to a totally different route after
completely closing off the area to any passing traffic. One of the final steps at
the scene is to clean up the crash site and return it to normal as soon as
possible.
Delays in traffic due to crashes are frustrating for the public and can lead to more
crashes. Drivers may be distracted by the crash or they may drive faster to make
up for lost time after passing the crash scene. Behaviors like these can lead to
additional collisions. Ensure you have the information you need to document the
crash then return the scene to as normal as possible allowing traffic to flow as
usual.
55
December 2009
SUMMARY
The at-scene investigation is the most important level of collision investigation.
Inadequate or incomplete documentation of the results of the collision severely
limits the extent to which a crash can be reconstructed. Follow-up investigators
and reconstructionists depend upon the data collected by the at-scene
investigator. Too often the at-scene investigator exhibits a lackadaisical attitude
towards taking measurements and collecting other evidence at the scene. These
investigators forget to take measurements or record them wrong or withhold
sketches and scale diagrams from the report. You must fight this urge when you
are at a scene where conditions are less than favorable. Follow-up investigators
and reconstuctionists are at the mercy of your investigation if any follow up is
required.
56
December 2009
Eleven – Step Summary
1.
Decide what results of the accident to
locate at the scene.






2.




4.

7.

8.
One spot for debris areas and clusters of
scars less than 3 feet long; bodies; detached
vehicle parts; pedestrian possessions,
irregularities and crossings of tire marks.
Two spots for each vehicular unit (trailers
separate), skid marks, curved tire marks less
than 6 ft. long, grooves or scrapes more than
3 ft. long.
Three or more spots for debris areas more
than 3 ft. long and at regular intervals along
yaw marks more than 8 ft. long.






Vertical measurements for edge of drop
off; temporary view obstructions, such
as vegetation and parked vehicles; fall
distance at construction sites, roadway
widths, distance between units, distance
between RP’s.
Make the additional measurements.

Record where convenient on field
sketch or by table of measurements.
10. Review field sketch and
measurement records for clarity and
completeness.
Coordinates with roadway edges as
reference line.
Triangulation with permanent landmarks as
reference points.
Combination of coordinates and triangulation.

Make desirable additions and
corrections.
11. Complete items of identification.





RP’s for coordinates.
Spots for vehicles or bodies which will be
removed before measurements are made.
Faint beginning and end of tire marks
(erasure).
Stations on reference line for long curved tire
marks.
On perimeter of debris area.
Others for convenience in referring to letter or
number designations.











Start field sketch.


To nearest half foot usually close
enough.
Use decimal point for feet and tenths,
underline inches, and spell out “steps.”
Decide what additional and
supplementary measurements are
needed.

9.
For coordinates three columns
SPOTS [N-S] [E-W]
For triangulation three columns
SPOTS [RP1] [RP2]
One horizontal line for each spot.
Make measurements and enter them
in table.

Mark spots on the road and roadside.


5.

Decide which system of measurements is
best.

Prepare table for recording basic
measurements.

Position of each vehicle and any body
outside of vehicle.
Scars (gouges and scratches) on the road,
roadside, and fixed objects.
Debris areas: significant vehicle parts and
pedestrian possessions; underbody dirt;
vehicle junk; liquid spatter, dribble, and
puddles.
Tire marks: skid marks, yaw marks, collision
scrubs.
Parked vehicles which may have obstructed
view.
Barricades and construction vehicles or
materials.
Decide what spots must be located for
each of the results.

3.
6.
Skeleton of roadway edges.
Dotted line to indicate edges aligned on
opposite sides of intersection.
Results of accident from Step 1.
Spots to be located from Step 2.
57
Sketch type (field or scale).
Nominal north direction.
Names of roads involved.
Description of RP’s.
If not at road junction, railroad crossing
or bridge, add distance and direction to
some such recognizable landmark.
City and/or county and state.
Time of day and date of crash.
Name of person making measurements.
Date of measurements actually made.
Crash or case number for reference.
Measured by (zero end & read end).
Document &/or case number.
Final positions & directions.
Grade.
Tire marks.
Label units.
December 2009
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December 2009
WISCONSIN MOTOR VEHICLE
ACCIDENT REPORT
OVERVIEW OF WISCONSIN ACCIDENT REPORTS (Document
and Debrief)
Wisconsin Motor Vehicle Accident Report Form (MV4000)
Most officers do not use the majority of traffic and safety responsibility laws every
day. You may feel it is not important to learn or understand them, however, if
you feel this way, you are wrong. Officers have a professional responsibility to
learn these things well enough that they can make correct decisions, give proper
advice, and enforce the laws effectively.
You already learned what actions to take at a crash scene to stabilize the scene
and collect evidence and measurements. The next step is documenting your
findings. Again, rely on the steps you learned up to this point to collect
information at the scene; do not rely on the Wisconsin Motor Vehicle Accident
Report Form to dictate your actions at the scene. Traffic-collision reports are
used to record routine data at a crash scene. An officer must complete a
Wisconsin Motor Vehicle Accident Report (MV4000) when a crash originates or
terminates on a traffic way, which involves at least one motor vehicle in transport,
and results in any of the following:
1. Injury or fatality of a person.
2. Total damage to one person’s property to an apparent extent of $1000 or
more.
3. Damage to government-owned property to an apparent extent of $200 or
more, except government-owned vehicles, which are $1000.5
If a crash meets any of these three criteria, an MV4000 must be completed by
the investigating agency. Filling out this form merely records specific data at the
crash scene. It does not constitute a full investigation of the crash. Law
enforcement officers must take other factors into consideration when
investigating a crash. The MV4000 should only be considered as part of an
investigation.
Law enforcement officers should use the Law Enforcement Officer’s Instruction
Manual for Completing the Wisconsin Motor Vehicle Accident Report Form when
completing an MV4000 form. This manual was developed to aid law
enforcement officers with completing the scannable MV4000 form. Officers
Division of Motor Vehicles. 1998. Law Enforcement Officer’s Instruction Manual for Completing the
Wisconsin Motor Vehicle Accident Report Form (MV4000). Page 2.
5
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December 2009
should use a #2 Pencil when completing the scannable MV4000 form and ensure
they fill the bubbles completely when asked to do so.
Information written on the form should be typed or printed in block-style,
uppercase lettering. Officers should double check each field for errors prior to
submitting the form. Reports submitted to the Traffic Accident Section at the
Bureau of Driver Services, Division of Motor Vehicles will be returned to your
agency if they need correcting.
Users of Traffic Crash Reports
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Drivers Involved
Owners of Property Struck by Drivers Involved
DMV Traffic Accident Section
DMV Uninsured Motorists Unit
Courts
District Attorneys
Defense Attorneys
Police Administration & Police Officers
Local Government Decision-Makers
Driver Educators
Emergency Medical Services Personnel
County Boards and City Councils
National Highway Traffic Safety Administration
Federal Highway Administration
Traffic Crash Reconstruction Specialists
County Traffic Safety Commissions
Traffic, Maintenance, and Design Engineers
DOT Bureau of Transportation Safety (BOTS)
DOT Highway Safety Strategies Section
State & Local Transportation Planners
Insurance Companies
DMV, i.e., points for traffic violations
Media
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December 2009
Figure 4-1 through 4-6 show examples of a completed MV4000 form and a
MV4000 Supplement Form (Wisconsin DOT).
(Figure 4-1)
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(Figure 4-2)
62
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(Figure 4-3)
63
December 2009
(Figure 4-4)
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December 2009
(Figure 4-5)
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December 2009
(Figure 4-6)
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Driver Report of Accident Form (MV4002)
If a collision is considered a “reportable accident,” and a law enforcement agency
does not investigate the accident, the operator of each motor vehicle is required
to complete a Driver Report Accident Form (MV4002). Inform the operators that
forms are available at police, sheriff’s departments, State Patrol districts, or
Department of Motor Vehicle customer service centers.
(Figure 4-7 Driver Report of Accident MV4002 – Page 1)
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December 2009
(Figure 4-8 Driver Report of Accident MV4002 – Page 2)
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Badger TraCS and the MV4000
Badger TraCS includes electronic report forms, including the Wisconsin Motor
Vehicle Accident Report (MV4000), the abbreviated MV4000 for single unit,
property damage vehicle/deer crashes, a form for amending previously submitted
MV4000s, a Uniform Traffic Citation, an Alcohol Incident Reporting form, A
uniform Municipal Citation, a Warning Citation, and an Attachment form to submit
photos and other supplemental information. TraCS runs on both stand alone
PCs and laptop computers in squad cars. This allows for immediate data entry in
the squad car or entry at a later time at your agency. Driver/vehicle information
can be replicated among forms, eliminating duplication of entry.
Reportable crashes can be submitted to the DMV/TAS electronically. Law
enforcement is able to archive crash data on their servers and generate copies
as necessary. The MV4000e contains all the fields on the MV4000 arranged in a
different order. The amended crash form is the same as the MV4000e, with the
addition of a Document Number Override field. This field contains the original
document number that is amended. Figure 4-9 is an example of Badger TraCS.
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December 2009
(Figure 4-9)
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December 2009
DRIVER, VEHICLE, ROADWAY, AND ENVIRONMENTAL
CONDITIONS AND FACTORS PRIOR TO THE COLLISION
Generally, information about the conditions prior to the collision are recorded on
the MV4000 by indicating which category in each of several classifications best
described the conditions of the driver, vehicle, roadway, and environment at the
location of the collision. Conditions refer to the officer’s observations. Factors
refer to the officers opinions. There are separate areas on the MV4000 for listing
this information; however, officers must understand the difference between
conditions and factors prior to completing the form.
Driver Condition
Driver condition data is based on your observations at the scene of the crash
and/or based on the chemical test results made available during the
investigation.

Presence of Alcohol or Drugs. For each operator or pedestrian involved in
the crash, determine if there is a presence of alcohol or other drugs. You
may have to get this information later if injured individuals were
transported to a hospital.

Driver actions. For each driver, determine what the driver was doing at
the time of the crash. For example, were they changing lanes, turning
right at a red light, etc?

Pedestrian actions. When a pedestrian is involved determine the location
of the pedestrian involved in the crash during the first harmful event. Also
identify what actions the pedestrian took that may have been a factor in
the crash. For example, did they disregard a signal, dart into the road,
etc?
Roadway Conditions
Road Surface Condition. If conditions suggest that some road surface condition
might have contributed, make a record of the actual conditions. Do not, at that
time, try to decide whether the condition actually did contribute to the crash. The
classification for road surface conditions is classified as: Dry, Wet, Snow/Slush,
Ice, Sand/Mud/Dirt/Oil, Other, or Unknown. More detailed descriptions of road
surface conditions that may lead to crashes are listed below.

Slipperiness: You should ask the question whether the slipperiness of the
road surface either surprised the driver or prevented successful evasive
tactics when the driver was confronted by a hazardous situation.
Conditions that make pavement slippery include: moisture, ice and snow,
loose gravel, leaves or grass – especially when wet, oil spots or grease,
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and asphalt or tar joints that are softened by hot weather. More often than
not, investigators will find no tire marks when slippery surfaces do
contribute to crashes. Do not let the lack of tire marks deter you from
considering slipping as a contributing factor.

Ruts: Are deep wheel tracks in hard material, usually ice, but sometimes
dirt. They contribute to crashes by interfering with normal control. Ruts
are much more likely to be a factor at high driving speeds. Be sure to
consider whether holes or ruts in the roadside or the shoulder were made
by the vehicle as a result of the crash or were they there before.

Holes. Holes in the paving have to be a foot or more long and wider than
a tire to be hazardous. Several small holes in a row can give enough of a
rough ride to make a driver lose control where a single hole would not.
When a tire hits a hole hard enough to be dangerous, you will sometimes
find evidence of the blow on the tire. Such marks confirm, rather than
prove, a conclusion regarding the hole as contributing to the crash.

Curbs. Curbs act like ruts. If a tire strikes one at an angle, you should
find scuff marks on the outside of the tire and probably will find them on
the curb. These marks often indicate where the vehicle went off the
roadway. When a vehicle strikes a curb at an angle and then swings
toward it so that both front and rear wheels strike, the wheel which strikes
first will nearly always leave a much more prominent sign of scuffing, both
on the tire and on the curb. This is because the first wheel strikes harder.
In most cases of this kind there is also a contributing driver action.

A Lip or Drop-off. A lip drop-off is simply a low shoulder at the edge of
hard pavement. It is more important when the shoulder is more than three
inches below the pavement, especially on concrete paving with a vertical
edge. Most crashes involving drop-offs occur when a driver tries to steer
back on the pavement without slowing enough. The lip acts as a rut or
rail, which keeps steering from being effective until the front wheels are
turned at a fairly sharp angle. Crashes that result from a car dropping off
the edge of the pavement are often detected by matching signs of it on the
inside of the front right tire and on the pavement edge. The drop-off may
occur a hundred feet or more before the point of collision.
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Soft Shoulders. Soft shoulders can cause the driver to lose control at high
speeds.
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Braking while partly on the shoulder. If the brakes are applied strongly
while the right wheels are on the shoulder and the left wheels are on the
pavement it will create a much greater drag factor on the left than on the
right. This difference in drag factors will cause the vehicle to rotate
counterclockwise with the result that it heads back across the road. The
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sidewise sliding on the shoulder will cause the wheels to dig in and the
vehicle may roll over. At speeds greater than 35 mph, especially if the
brakes are released, the vehicle will suddenly go across the road to the
left.
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Traffic Control. If traffic control devices are present at the scene of the
crash, you should record their condition and visibility for those drivers who
are required to respond to them. These devices include signs, signals,
pavement markings, speed limits, prohibited turns, one way streets, etc.
Exactly what descriptive data are required depends on the circumstances
of the crash. For example, there are some collisions in which the timing of
the traffic signals is important and must be observed and recorded.6 This
is especially important if you decide to initiate any enforcement action
based on the driver failure to respond to them.
Environmental Conditions.7

Light Condition. The road or anything connected with it may be
temporarily modified by conditions existing at the time of the collision.
Light condition is usually classified according to three categories: Daylight,
Dawn or Dusk, or Darkness.

Visibility/Weather Conditions. Visibility may change quickly so you must
note it as soon as possible. Low visibility is usually created by darkness,
fog, snow, falling rain, glare from the sun, or other atmospheric conditions.
When visibility is low, objects gradually become visible as they loom up in
the distance.

View Obstructions. Unlike objects that gradually appear due to reduced
visibility, if the view of an object is obscured, the hazard appears rather
suddenly from behind or from the back of a solid object. The best way to
evaluate the view is to put yourself in the driver or pedestrian position.
View obstructions on the road are usually vehicles, either moving or
parked. They can prevent drivers from seeing signals, signs at the
roadside, other vehicles, or pedestrians.
CONTRIBUTING CIRCUMSTANCES TO A CRASH
You will be asked to provide your opinion in three areas on the MV4000. Based
on your observations and the information collected at the scene provide your
opinion on any driver factors, vehicle factors, or highway factors that may have
contributed to the crash.
6
7
Baker, Kenneth, S. (2001) Traffic Collision Investigation. P. 172
Baker, Kenneth, S. (2001) Traffic Collision Investigation. Pg. 172 - 173
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Driver Factors
Observe each operator or pedestrian involved in the crash. Determine if the
individuals appear to be normal, have reduced alertness, or are impaired. On the
MV4000, fill in the bubble that best describes the driver or pedestrian’s
appearance. There may be instances when you are not able to observe the
driver’s condition, for example, during Hit & Runs, if the driver leaves the scene
prior to your arrival, etc.
You will also offer your opinion about what the driver may have done to
contribute to the crash. For example, from the information you gather, you may
feel that the driver was exceeding the speed limit or driving too fast for
conditions. Consider your observations and facts then formulate your opinion
and document it on the MV4000.
Vehicle Factors
After inspecting the vehicles involved in the crash, determine if some sort of
vehicle malfunction contributed to the crash. Examples might include, faulty
brakes, a blown out tire, a burned out turn signal or failure of head lamps, etc.
Again, this is your initial opinion about the vehicle based on your findings at the
scene.
Highway
In your opinion, list any highway factors that may have contributed to the crash.
These include factors like the highway being wet from snow or rain, or was there
ice that one or more of the vehicles could have slid on. Were there any issues
with the road itself, such as a narrow, low, or soft shoulder, loose gravel, rough
pavement or debris in the road that caused the vehicle to swerve, etc? Fill in the
appropriate highway factors that may have contributed to the crash in the
appropriate block on the MV4000.
SUMMARY
The Traffic Accident Section (TAS) of the Wisconsin Department of
Transportation receives the Wisconsin Motor Vehicle Accident Report (MV4000)
from all law enforcement agencies. Periodically MV4000’s are returned to the
reporting agency due to incomplete or inconsistent data. Correcting, returning,
and following up on the MV4000 can be time consuming for all parties involved.
Check for errors prior to submitting your reports. This will prevent the need to
return crash reports and save time spent making corrections. Some of the top
reasons for MV4000 returns are:
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Injuries in field 7 do not match injuries in fields 38 and 70.
Vehicle or owner information is missing.
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8
Power unit not listed for trailers legally parked along highways or
roadways.
Incorrect date of birth or drivers license number.
Illegally parked vehicles.
Missing driver information for driverless motor vehicle crashes.
Incorrect vehicle information.
Dealer plate with owner listed as individual.
Double deer hit. If two vehicles hit the same deer, vehicle information is
required for both vehicles.
Drivers listed in the driver area who are under the age of 7.8
Wisconsin Department of Transportation, Traffic Accident Section. Crash Chronicle. Summer 2004.
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PHOTOGRAPHING THE SCENE
CRASH SCENE PHOTOGRAPHY
Crash scene photography is fundamental to the preservation, evaluation,
interpretation and presentation of physical evidence. In many instances,
photographs can describe objects better than words. Photographs are used in
conjunction with measurements and well written reports to capture the results of
a crash. A traffic crash photographer’s goals include producing accurate,
detailed images that record the locations, conditions and reflect evidence as
clearly and objectively as possible.
There is a wide variety of equipment and procedures available to law
enforcement officers for the purpose of taking photographs. Your agency’s
equipment may include either film or digital imaging and may produce still images
or video images. Whatever media you use to capture images, officers can
expect to be called upon in court to verify that the images/photographs accurately
represent the scene and the event at the time of the photographer’s
observations.
Use of Photos
People tend to believe that “photos do not lie.” Even though a photo might not be
a completely “true representation,” it is regarded as relatively free from bias that
my influence verbal or written reports. Photographs refresh the memory about
something seen in the past and often make notes and observations unnecessary.
A spare photo can be marked making the photo more effective in reminding you
of what you observed. It is also useful to mark each photo of a collision scene
with a small arrow to show which direction is north.
Misused Photos
Investigators can be led astray by the obvious advantages of photography in a
collision investigation. Photographs should not be used as an easy way out of
arduous observing and measuring. An investigator should think of photos only
as a means of recording what he or she thinks is important. He or she should
avoid taking pictures as a substitute for observations and not expect to find in a
picture what he or she failed to note before making the picture.
Anyone who has ever tried to make a map from a photograph knows why photos
are not adequate substitutes for measurements. It is true that by
photogrammetry, maps can be made from photos, but this is a tedious and
expensive process. Therefore, photos supplement but are not good substitutes
for written notes, classification of damage, description of the collision location,
measurements, and above all careful observations by the investigator.
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Spare photographs may be marked as you please, but otherwise mark other
photographs in only one of three ways:
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On the back.
With a soft “china-marking” crayon which can be cleaned off easily.
On a transparent or translucent overlay, either tracing paper or acetate.
Photos marked with pens or felt-tipped markers are ruined for some purpose.
Consider using a spare photograph or mark a copy made from a copy machine.
“AT SCENE” PHOTOS
Basic “At-Scene” Photos
The particular purpose of at-scene pictures is to show how the situation looked
when vehicles came to a rest after the crash, how objects were arranged and
how things were related to each other. These photos enable anyone interested
to see quickly how pictures of specific details relate to the whole crash scene.
Following a preliminary evaluation of the scene, officers will be called upon to
take scene photos in a series of overviews, mid-range views, and close-ups if
necessary. Generally speaking, a photographer will have four overall views of a
crash scene. These are usually taken from 150 feet or further from the crash
scene. Then, medium views will cover the entire roadway width at or near the
area of impact. Also, consider one photo to represent each driver’s/participant’s
view as they approached. It is helpful to try to take these photos from the
participant’s actual view. For example, a photo from 36 to 42 inches above
ground level might reasonably simulate a driver’s perspective while seated
behind the wheel of an average car. And lastly, consider the best overall picture
of the scene. This single representation seeks to include all vehicles, all the
results and some distinguishing landmark to help represent things in the best
possible perspective.
To completely document a crash scene photographers should try to reflect what
shows on the roadway. This includes skid marks, yaw marks, any other kind/s of
tire marks, and both solid and liquid debris. The photographer’s goal is clearly to
show what is there but in some cases it might be just as important that photos be
used to document what is not present at the time of the investigation.
In Figure 5-1 position A gives a view straight down the road, includes both cars,
some debris, and a landmark stop sign; the Ford obscures most of the Chevrolet
and all tire marks. Position B is a good view of the right side damage of the Ford,
but it does not show whether the vehicles are actually touching each other. The
tire marks and stop sign are too far to be clearly visible. Position C is a good
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view of damage to the left side of the Chevrolet. It clearly shows that the cars
are still engaged, but it omits the tire marks and both landmark stop signs. It
does not show the position on the road well. Position D includes everything but
is so far off (more than 80 ft) from anything significant to be very useful.
The angles included in these undesirable views are shown as dotted lines in
Figure 5-1. Position E shows everything that Position D does, but better. It is
close enough to show the tire marks well. It also shows major debris. Aimed
straight down the middle of a lane, it shows the position of the vehicles on the
road and indicates that they are engaged. This is the best overall picture.9
C
STOP
D
.
A
E
F
SKID
STOP
0
10
20
DEBRIS
CHEVROLET
FORD
.
30
B
SCALE
Baker, K. S. (2001) Traffic Collision Investigation, p. 264
(Figure 5-1)
Photographs can help identify the location of marks on the road. You can do so
by:
 Including a nearby landmark, or
 Capturing two images – one of the item of interest accompanied by one
which includes a background object that relates the item to the scene, or
 Including some kind of an identifying mark within the photograph.
For the purpose of documenting long marks, typically 40 feet or more in length,
you should begin by photographing the start of the mark, the end of the mark,
and any peculiarity in between. You should also consider photographing the
mark at regular intervals along it. And you should pay special attention to any
9
Baker, K.S. (2001) Traffic Collision Investigation, p. 263 – 264
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December 2009
changes in direction or peculiar areas in the texture of the road. For example if
the road changes from concrete to asphalt you would pay special attention to that
location where the tire mark switches from one to the other.
Photographing Vehicle Damage
Photos are a particularly useful way to document vehicle damage. In order to
reconstruct the event and to evaluate cost to repair, these photographs are
generally best done at the scene. Most crash investigation vehicle damage
images can be documented in a standard record of four photos. Starting at the
front of the vehicle align your photograph along the vehicle’s center line and
begin with one photo of each side working clockwise and standing squarely along
the end or side of the unit. You may align the camera by using undamaged parts
to give your best possible perspective.
The four standard pictures of vehicle damage.
(Figure 5-2)
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On completion of these four photos (one of each side), consider taking the one or
two photos that best reflect damage to a vehicle. Once you have your overview
of general damage, consider details which might be documented in photos.
Some details of damage may include:
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Imprints of one vehicle on another
Friction and or abrasion marks
Damage to lamps
Damage to loads
Sources of injury to pedestrians or occupants
Detailed damage to tires, wheels, and the underside of the unit.
If a particular location on the car has some area of interest or evidence, like a
light bulb distortion or paint transfer, close ups need to be taken. To do this,
three standard photographs will be needed. The first shot is of the overall side of
the vehicle, the second shot is closer to the area of interest, and the third shot is
then a close up of the item of interest. Depending on what the item is, you may
want to repeat these steps placing a scale near the item.
Photographs should be taken that would include any vehicle defects such as bald
or worn tires, dirty or cracked windshields, or any pre-crash damage that could
have contributed to the crash. Also take photographs of any vehicle
modifications or aftermarket items that are on the vehicle; especially those
suspected of contributing to the crash or altered the original specifications of the
vehicle.
Last but not least would be photographs showing any interior damage sustained
during the collision. Occupant-to-vehicle impacts are very useful in establishing
occupant pre-impact seating positions. It is for this reason that photographs
showing interior damage or implements of injuries to passengers be captured
through photography.
Procedures for Photographing a Crash Scene
There are a variety of specific photos and considerations that might assist you in
an investigation. Remember, if you need to photograph a vehicle’s interior, make
your exposure as if there were no daylight. When photographing during hours of
darkness, most camera flash units are only effective for about a maximum of 12
feet and reflective surfaces may be difficult or impossible to distinguish with use
of a flash. Similarly, use of a flash during daylight hours may reveal things in
shadow, such as underneath a vehicle that would otherwise not be visible. You
may find an assistant useful to help point out specific things such as vehicle
identification number plates, matched areas of damage between different
vehicles, or some other specific evidence being portrayed in the photo.
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Take un-scaled photographs first, then introduce your scale and take another
photo of the same visual image. Chalk items before moving them and then
photograph the area chalked again. When you remove an item of evidence,
photographing the surface underneath the item may avoid questions later.
Always be cognizant of visibility conditions and/or obstructions such as fog, traffic
control devices, parked vehicles, signs, or window conditions which may have
been relevant to the participants in the crash. Photographs may be able to help
you document a victim’s location and injuries when appropriate. A given
vehicle’s condition can be documented as it might relate to the contents, tire
condition, or any other indication that the vehicle may have been unsafe prior to
the incident.
When taking the photographs try to avoid dramatic shots. Those showing
excessive amounts of blood and gore are seldom useable in court. Despite what
can be seen on television or at the movies these days, some courts frown on
graphic photographs that might prejudice the jury. There are times, however,
when those photographs have a purpose and if your intent is to show a position
or implement of injury they are of use and should be taken. It is a common
practice to take photographs of fatal victims in their final rest position and after
being removed from the vehicle for evidentiary and identification purposes.
Try to avoid shots containing emergency vehicles and equipment. Seldom is it
useful and most often they block important features that need to be viewed, if
nothing else to show relationships. A tire mark obscured by emergency vehicles
may miss some important characteristics of that mark which might be needed to
help identify it properly.
OTHER CONDITIONS DEALING WITH PHOTOGRAPHY
TIPS/Techniques
The following are techniques that you may find helpful to make your pictures
more useful. The application of these techniques is dependent on what type of
camera equipment you will be assigned or using.
The use of “fill flash” is a technique used to eliminate shadows when taking
daytime photographs. Most cameras allow for this feature. By using the
cameras flash during the day, it sends light into areas that normally would be
shadowed or covered by the normal light. The areas that would show up on a
normal picture dark now show detail. This works in areas where you have
under-ride damage under a hood or bumper, on the underside of a vehicle, or in
wheel well like when photographing the tread on a tire.
Avoid pointing your camera directly at shiny objects such as chrome or glass
when using flash photography. If you must use a flash, the light should be cast
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from the side or at an angle. If you shoot the flash directly at the shiny object,
you will get flashback, which burns out the detail of the object.
When taking photographs of glass and other transparent items such as
instrument panels, consider the use of a polarizer. Polarizers reduce glare.
Using a polarizer allows the ability to see detail behind the glass. Examples of
this are when photographing a V.I.N. plate on a dash, hair or tissue on a
windshield star, or speedometer or tachometer needle setting in a dash.
Another useful area for polarizers is for enhancing color contrast. Polarizers
separate and contrast like colors. Examples of where this is useful is when
locating and photographing tire marks or road scars on a roadway, or when you
have paint transfer on colors that are very similar.
SUMMARY
As you can see by this chapter there is more to taking pictures then pointing at a
subject and snapping the shutter. It is important you understand when to take
photographs and what to take photographs of. Many different people use the
photos you will be taking and they are just one of the steps in providing a
complete professional investigation.
Your agency will provide you with additional guidelines and requirements that
you will have to follow when taking pictures. You should read the owners manual
for your particular equipment and become familiar with its operation. When you
are at a crash scene and traffic is backed up or the weather is bad is not the time
to be stumbling around in the use of your camera or other equipment.
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APPROPRIATE ENFORCEMENT
ACTIONS
PROCEDURES TO DETERMINE SPEED ESTIMATES
Knowing the initial speed of a crashed vehicle can be of great value to the
investigator in reconstructing what happened and why. Drivers may not admit or
even know their actual speed at the time of the crash and many times the speed
estimate of witnesses is unreliable. A scientific method which eliminates much of
the guesswork is that of computing initial speeds from the measured length of
skid marks left by tires sliding on the pavement.
The actual computation of speed from skid marks is a specialized skill involving
the use of complex mathematical formulas and is beyond the scope of this text.
The basic methods of computation, however, are outlined in Appendix B. This
section covers the theory behind the computations and the methods of collecting
evidence to be used in such calculations.
Excessive speed or driving at speeds too great for conditions is a common cause
of crashes. When faced with an emergency, a driver will usually apply the
brakes with maximum force. The driver may also swerve the vehicle sharply.
The resulting skid marks provide evidence which can be used to compute, with
reasonable accuracy, the initial speed of the vehicle. As long as your
measurements are accurate, a reconstructionist will be able to estimate the
vehicle’s speed prior to the crash.
ENFORCEMENT ACTIONS
As with any other incident you are dispatched to investigate as a law
enforcement officer, traffic crashes may require you to take some form of
enforcement action. After you have obtained all the facts, evidence and
statements available to you, the enforcement action you take will be dictated by
traffic law, department policy and common sense. It is important that you
complete your investigation before making a decision regarding who is, or is not,
at fault or if both parties are to blame for the crash. Do not jump to any
conclusions or make any premature statements.
Commonly, issuing a traffic citation to the at fault driver prior to returning to your
assigned patrol duties will be the enforcement action you take, if any at all.
Department policy, a comprehensive knowledge of traffic law, and common
sense will all be factors in your enforcement decision.
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Some crashes, such as OMVWI or crashes that result in injury, death, or
substantial property damage may require additional investigation. Often these
crashes will require you to complete a detailed report to be forwarded to the
District Attorney (DA) pending review for criminal charges.
You will need to accurately document all the facts regarding a crash in order to
prevail in court if your DA charges a driver for a criminal violation. Your report
will impact criminal proceedings and any civil litigation. It is critical that you have
conducted a thorough and detailed crash investigation. Criminal and civil cases
may take several years to come to trial requiring you to depend on your reports
to provide credible testimony.
The thoroughness of your report will reflect on you as the investigating officer.
Your professional reputation is important. Be sure you gather all the facts and
are fair to all parties involved or affected by the crash.
All conclusions and actions must be based on the facts, evidence, and
statements you personally have gathered or know to be true. You are not the
agent for the insurance companies. You are an impartial taker of the facts. Do
a professional investigation as a law enforcement officer.
ENFORCEMENT DECISION
After you have gathered all the facts and information regarding a crash you will
need to make a charging decision. You will essentially have four options.
OPTION #1: No Formal Enforcement Action
Examples of crashes that you may decide not to take enforcement action on
would be:
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A “slide off” in bad weather resulting in minimal damage, yet sufficient
enough to be a reportable crash;
A reportable non-injury crash where a driver hit debris on the roadway
during night time or other conditions of reduced visibility;
A reportable crash where conditions a normal driver would not be aware of
existed;
Striking livestock that entered the roadway that would have been
unavoidable by the driver;
A car vs. deer crash.
OPTION #2: Issue a Traffic Citation
If there is not serious injury or death, moderate property damage, no criminal law
violation or other extenuating circumstances you might issue a Wisconsin
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Uniform Traffic Citation (WUTC / MC4016). Examples of crashes that you may
decide to issue a WUTC would be:
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Stop sign violation;
Wrong way on one-way street;
Excessive speed for road / traffic conditions;
Inattentive driving (i.e.: falling asleep / cell phone use)
OWI 1st offense
OWI with passenger under 16 years of age;
Absolute sobriety violations;
Failure to report traffic crash.
OPTION #3: Criminal Violations
Serious crashes may require you to forward your completed investigation report
and charging recommendation to the DA for review and determination whether
criminal charges are issued. Generally crashes involving serious injuries,
fatalities, extensive property damage or unusual circumstances will fall into this
category.
These crash reports may require the assistance of a traffic crash
reconstructionist, detectives or other specialists to complete.
Examples of Criminal Violations are:
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Homicide by intoxicated user of a motor vehicle;
Injury by intoxicated use of a vehicle;
Crash as a result of a pursuit;
Criminal OWI violations.
Non-Contributing Violations
Violations for traffic law violations that may not have directly contributed to the
crash should also be enforced. Although these violations may not have been a
direct cause of a crash, they are violations and should be enforced.
Examples of these violations are:
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OAR / OAS;
Vehicle registration violations;
Financial responsibility violations;
GDL violations;
Seatbelt violations;
Child restraint violations;
Open intoxicant or other alcohol violations.
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Generally, as a law enforcement officer you will have a great deal of discretion as
to what enforcement action you will take at the scene of a crash. If there were
factors that would make a reasonable person believe the crash was unavoidable
you would probably be on solid grounds for issuing a traffic citation.
It is important that you do not prematurely form an opinion regarding who or what
caused a traffic crash. It is equally important that you, as the law enforcement
officer investigating a traffic crash, remain neutral and not make comments
regarding the cause of a crash until you have gathered all the information
available as they relate to the crash.
Hastily spoken words can make enforcement action more difficult if drivers,
occupants or witnesses agree with your original comment that was based on a
quick opinion rather than facts. If you were incorrect in your assumption you may
have a difficult time if you are challenged in court by drivers or other persons who
heard your erroneous comment based on a too quick assumption of what
happened.
You need to determine what your intent is when you issue a written citation at a
traffic crash as with any other type of traffic contact. Are you attempting to
correct driving behavior or simply penalize a driver for a traffic violation? Your
primary objective should be to correct bad driving habits or behavior.
HIT-AND-RUN INVESTIGATIONS10
The first steps in most hit-and-run investigations are the same as those in the
investigation of any collision. Get to the scene safely and quickly and handle
emergency problems. If you know before reaching the scene that the collision
may be a hit-and-run case, watch for vehicles coming from the direction of the
collision. Note descriptions and registration numbers if possible. One of these
may be the vehicle involved.
At the scene, try and locate the drivers as soon as possible. If a driver cannot be
quickly located, consider the possibility of a hit-and-run. Lose no time in stating a
search for the missing driver. Get the best description possible of the missing
vehicle and occupants. These may eventually lead to the driver. Communicate
available information to a police dispatcher who can broadcast the description in
the area. As soon as all available information about the missing driver has been
obtained, go ahead with other steps of the investigation at the scene.
Hit-and-run driving may be either a felony or a misdemeanor. In cases resulting
in injury or death, it is a felony. It is a misdemeanor where only property damage
10
Schultz, D. and Hunt, D. (1998) Traffic Investigation and Enforcement. p. 217 – 222.
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is involved. In either case, the incident should be investigated just as any other
crash, except that special hit-and-run procedures should be followed.
The officer investigating the hit-and-run is really conducting two investigations in
one – to determine the cause of the crash and to determine the identity of the
driver who has left the scene. It is one type of crash in which it is readily
apparent that a violation has already occurred – that of evasion of responsibility.
The officer, however, must not lose site of the fact that leaving the scene is not a
cause of the crash. The investigation must be thorough in order to uncover the
cause of the crash as well as to locate the missing driver.
Time is important in hit-and-run investigations. The longer it takes to locate he
driver, the more time he or she will have to repair any damage to the vehicle,
destroy evidence, and establish an alibi. Therefore, the initially responding
officer faced with a hit-and-run investigation should broadcast this information for
the benefit of other police units as quickly as possible so that a wide search for
the violator may be put into motion.
It is not uncommon for a drunk driver to flee the scene of a hit-and-run incident
either in the vehicle or on foot. The motive here is to avoid being charged with
driving under the influence. Unless the driver is located quickly, any tests done
to indicate driving under the influence may not be useful or incriminating. It is
also not uncommon for drivers of stolen vehicles or drivers involved in other
crimes to flee the scene of a collision for obvious reasons.
You should then proceed to interview any witnesses in more detail and try to
obtain more details about the suspected vehicle and/or driver. You should try to
determine if the suspect stopped at any time and if so did he/she talk to anyone?
Any new information should be reported to dispatch so other units involved in the
search may be advised. You should be alert for the return of the responsible
driver to the scene to mingle with the crowd to see how the investigation is
progressing – even going so far as to follow the officer very closely. The
inquisitive person who displays an unusual interest in the progress of the
investigation might well be the driver involved who is attempting to discover how
close the investigation is coming to making and identification.
In addition to these steps, process the scene as you would with any other
collision. Document and measure the scene and complete the appropriate
paperwork. Follow-up activity will include checking garages, wrecking
establishments, service stations, and body shops, and putting them on alert for a
wanted vehicle. Good hit-and-run investigation and reporting means digging a
little deeper to obtain more facts. It is the small detail that might be easily
overlooked which, if found and checked, will lead to the apprehension of the
suspect.
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SUMMARY
You will respond to a number of traffic crashes during your career as an officer.
The conditions when responding to a scene are usually stressful and unpleasant
experiences for everyone involved, however, you have a responsibility to
properly record all of the facts surrounding the crash. Often times, you are the
only person who is not emotionally attached at the scene and are the one person
everyone at the scene is looking to for direction. Using the RESPOND model will
help you stabilize the scene and get help for any injured or get any other
resources needed to help at the scene.
This text introduced you to the basic skills and steps to follow when responding
to cash scenes and investigating crashes. You learned the basic at-scene
investigation techniques, including how to properly measure and document the
scene. The accuracy with which you measure and document the scene will
directly affect any advanced investigations or reconstruction so it is important that
you take your time and follow the processes outlined in this text when measuring
and documenting a scene and when completing the Wisconsin Motor Vehicle
Accident Report (MV4000).
You did not learn any advanced techniques or reconstruction techniques. This
level of investigation takes more training and experience. That does not mean
the skills you learned are any less important, however. Any follow on
investigations rely heavily on the work you complete at the scene. It is important
for you to take your time and document the scene accurately. This text only
introduced you to the basics; if you find yourself on a major scene you should
follow your department policy and consider requesting help from a more
experienced investigator.
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APPENDIX A - GLOSSARY
ACCELERATION – The time rate of change of velocity; change of velocity
divided by time; a vector quantity measured in feet or meters per second per
second or expressed as a decimal fraction of acceleration of gravity. Positive
acceleration increases the velocity of a body, negative acceleration
(deceleration) reduces the velocity of a body.
ACCELERATION SCUFF – A scuffmark made when sufficient power is supplied
to the driving wheels to make at least one of them spin on the road surface.
ACUTE ANGLE – An angle that is less than a right, 90-degree, angle.
AFTER-COLLISION SITUATION MAP – A scale drawing of the scene after a
traffic collision situation has stabilized; a geographical summary of results of a
collision without indication of any assumed events of the collision or other
inferential elements.
ANGLE COLLISION – A collision between two traffic units approaching on
separate roadways or other paths that intersect.
APEX – The point at which two sides of an angle meet or cross.
ARC – A part of a curve, especially part of a circle, between two points on the
curve.
AT-SCENE INQUIRY – Questioning informants at the scene of a traffic collision
for the purpose of obtaining facts required for the official collision report and such
other information as may be readily available.
AT-SCENE INVESTIGATION – Examining and recording results of the collision
and obtaining additional information at the scene of a traffic collision which may
not be available later and which supplements data obtained for the collision
report. The information obtained is as factual as possible.
ATTRIBUTE – Any inherent characteristic of a road, a vehicle, or a person that
affects the probability of a traffic collision.
BALLAST – Selected material placed on the roadbed to hold track in line. Ballast
preferably consists of hard particles easily handled in tamping, which distribute
the load, drain well, and resist plant growth.
BITUMINOUS CONCRETE – Concrete cemented with a bituminous material
such as tar or asphalt.
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BODY TYPE – The general configuration or shape of a vehicle distinguished by
characteristics such as number of doors, seats, or windows, roof line, hardtop,
convertible, etc.
BRAKING DISTANCE – The distance through which brakes are applied to slow a
vehicle; the shortest distance in which a particular vehicle can be stopped by
braking from a specified speed on a particular surface; the distance from
application of brakes to collision.
BRAKING TIME – The time required to traverse the braking distance.
CAUSE ANALYSIS – The effort to determine, from whatever information is
available, including results of collision reconstruction, why the collision occurred,
that is, the complete combination of circumstances that caused the highway
transportation system to break down at the time and place of the collision.
Cause analysis has been referred to as determining “indirect” or “condition”
causes.
CENTERED FORCE – A force directed toward the center of mass of the vehicle
or other object in a collision.
CHIP – A short, deep gouge; a hole in the pavement made by a strong, sharp,
pointed metal object under great pressure, usually without striations.
CHOP – A broad, shallow gouge, even and regular on the deeper side and
terminating in scratches and striations on the opposite, shallower side; a
depression in pavement made by a strong, sharp metal edge moving sideways
under heavy pressure.
CHORD – A straight line connecting the ends of an arch or two points on a curve.
A chord is never greater than the diameter of a circle of which the arc is part.
COEFFICIENT OF FRICTION - The drag factor created by a surface causing a
body sliding across it to slow it down; represented by a number, usually a
decimal less than 1.00; and used in calculating speed from skid marks.
COLLISION RECONSTRUCTION – The effort to determine, from whatever
information is available, how the collision happened. Reconstruction was
formally referred to as determining “behavioral” or “mediate” causes of a collision.
COLLISION SCRUB – A short, usually broad, skid mark or yaw mark made
during engagement of the vehicles in a collision.
CONCRETE – A paving material consisting of an aggregate of stones of
assorted sizes held together with a cement binder; bituminous concrete, Portland
cement concrete.
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CONTACT DAMAGE – Deformation or defacement resulting from direct pressure
of another object or surface in an impact, direct damage. Compare with induced
damage.
COORDINATE MEASUREMENTS – A method of locating any spot in an area by
two measurements from the nearest point to the spot on a specified reference
line; 1) the distance and direction from that point to the spot, and 2) the distance
and direction from that point to a specified reference point on the reference line.
CRASH – The collision of a vehicle with another vehicle, a person, a fixed object,
or a vehicle rollover.
CRASH INVESTIGATION – The systematic collection of evidence, the
examination of information, and the recording of data to identify crash factors.
CRASH REPORTING – The standardized method of recording crash data
derived from a crash investigation.
CRASH SCENE SPECIALIST – An officer who has been provided advanced
training to conduct supplementary investigations of serious crashes, to gather
data and evidence in more depth than the on-scene investigator, and to follow up
on unresolved issues.
CROOK – An abrupt change of direction of tire mark due to collision forces. The
crook often indicates the position of a tire at first contact.
DEBRIS – Loose material scattered about at the scene as a result of a traffic
collision; dirt, liquids, vehicle parts, cargo, personal belongings and other things.
DISCRIMINATIVE REACTION – A reaction to perception of an unfamiliar hazard
or other situation which requires additional information than that immediately
available to make a decision or which presents several choices of possible
evasive tactics.
DRAG FACTOR – A number representing the acceleration or deceleration of a
vehicle or other body as a decimal fraction of the acceleration of gravity; the
horizontal force needed to produce acceleration in the same direction divided by
the weight of the body to which the force is applied. When a vehicle slides with
all wheels locked, on a level surface, the coefficient of friction and the drag factor
have the same value.
DRIBBLE – Liquid debris from a vehicle or its cargo that drops to the ground,
often leaving a trail, if the vehicle is moving, from a spatter area to a puddle.
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DROP OFF – The edge of pavement where it is more than about 2 in (about 5
cm) higher than the abutting shoulder.
ECCENTRIC FORCE – A force which is not toward the center of mass of the
vehicle or the center of mass of the other object in a collision.
EDGE LINE – A line which indicates the edge of the roadway.
EXTRICATION – The removal of a victim trapped in a motor vehicle or in a
dangerous situation.
FALL – A downward and onward movement in the air under the force of gravity
after forward momentum carries an object beyond its supporting surface.
Rotation during a fall is gradual and the object usually lands right side up.
FIELD SKETCH – A freehand map of the scene or site of a collision showing
certain features of the collision or road configuration, usually for the purpose of
recording measurements.
FINAL POSITION – The exact location of a vehicle or body after a traffic
collision.
FIRST CONTACT POINT (FCP) – The exact point on a vehicle, pedestrian, or
other objected touched in a collision or the place on the road or ground closest to
the first contact between colliding objects. Sometimes called point of impact or
collision point.
FIRST HARMFUL EVENT – The first occurrence of injury or damage.
FLAT-TIRE MARK – A scuffmark made by an overdeflected tire; a mark made by
a tire which is under inflated or overloaded.
FLIP – A sudden upward and onward movement off the ground when an object’s
horizontal movement is obstructed below its center of mass by an obstacle on
the surface supporting the object.
FRICTION MARK – A tire mark made when a slipping or sliding tire rubs the road
or other surface.
FULL IMPACT – An impact during which motion momentarily ceases between
some area of the colliding objects while they are in contact with each other. If the
colliding objects do not separate after the collision, the impact is complete.
GAP SKID – A braking skid mark which is interrupted by release and reapplication of brakes or which terminates by release of brakes before a collision.
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GORE – The area immediately behind the bifurcation of two roadways, bounded
by the edges of those roadways; the angle between two roadways where one
roadway divides into two.
GOUGE – A pavement scar deep enough to be easily felt with the fingers; chip,
chop, or groove.
GRADE – The change in elevation in unit distance in a specified direction along
the center line of a roadway or the path of a vehicle; the difference in level of two
points divided by the level distance between the points. Grades are designated
in feet (meters) of rise or fall per foot (meter) of level distance or in rise or fall as
a percent of the level distance. Grade is positive (+) if the surface rises in the
specified direction and negative (-) if it falls in that direction.
GROOVE – A long, narrow, pavement gouge; a channel in the pavement made
by a small, strong, metal part being forced some distance along the surface while
under great pressure.
HATCHING – Shading consisting of closely spaced parallel lines in a drawing.
HAZARDOUS MATERIAL (HAZMAT) – Any chemical substance or material that
can pose a threat to health, safety, and property.
HAZARDOUS MATERIAL INCIDENT – Any situation that deals with the
unplanned release of hazardous material.
HIGHWAY - All public ways and thoroughfares and bridges on the same. It
includes the entire width between the boundary lines of every way open to the
use of the public as a matter of right for the purposes of vehicular travel. It
includes those roads or driveways in the state, county or municipal parks and in
state forests which have been opened to the use of the public for the purpose of
vehicular travel and roads or driveways upon the grounds of public schools, as
defined in s. 115.01 (1), and institutions under the jurisdiction of the county board
of supervisors, but does not include private roads or driveways as defined in sub.
(46).
HIGHWAY INCIDENT - Any event that disrupts the normal flow of traffic.
HYDROPLANING – Skidding on water. Tires ride on water film.
IDENTIFICATION – Designation of a road location, a vehicle, a person, or a
traffic collision in such a manner as to positively distinguish it from all others of
the same description. Identification is often accomplished by a unique number
such as a vehicle identification number, registration number, or a driver’s license
number.
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IDENTIFYING NUMBERS – Numbers and letters, if any, on a vehicle designated
by the Department of Transportation for the purpose of identifying the vehicles;
VIN is not the registration number.
IMPACT – The striking of one body against another; a collision of a vehicle with
another vehicle, a pedestrian, or some other object.
IMPRINT – A mark on a road or other surface made without sliding by a rolling
tire or a person’s foot. An imprint usually shows the pattern of the tire tread or
shoe that made it.
INCIDENT COMMAND SYSTEM (ICS) – A system used to manage resources,
such as personnel, equipment, and supplies, at the scene of an emergency.
INCIDENT COMMANDER – The person in the incident command system
ultimately responsible for managing and directing an emergency response.
INDUCED DAMAGE – Damage to a vehicle other than contact damage. Often
indicated by crumpling, distortion, bending, and breaking. Induced damage
includes damage done by another part of the same vehicle. Compare with
contact damage.
INFORMANT – Any person who communicates information.
INFORMATION – Any knowledge received concerning a particular matter, such
as a traffic collision, from any source, regardless of the reliability of the
knowledge.
INTENDED COURSE – The path that would have been followed by a traffic unit
as a normal part of its trip had the situation hazard not led to evasive tactics or
collision.
INTERCHANGE – A system of interconnecting roadways in conjunction with one
or more grade separations, providing for the movement of traffic between two or
more roadways on different levels.
INTERSECT – The point at which two straight lines, such as the extensions of
two roadway edges, cross each other; the apex of the angle formed by two
straight lines which cross. Also called point of intersection.
INTERSECTION – The area embraced within the prolongation or connection of
the lateral curb lines, or, if none, then the lateral boundary lines of the roadways
of two highways which join one another at, or approximately at, right angles, or
the area within which vehicles traveling upon different highways joining at any
other angle may come in conflict. Where a highway includes two roadways 30
feet or more apart, then every crossing of each roadway of such divided highway
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shall be regarded as a separate intersection. In the event such interesting
highway also includes two roadways 30 feet or more apart, then every crossing
of two roadways of such highways shall be regarded as a separate intersection.
JUNCTION – The general area where two or more highways join or cross within
which are included the roadway and roadside facilities for traffic movements in
the area. A junction may include several intersections of roadways.
LAST CONTACT – The final touching of objects in a collision before separation;
the time and place on a traffic unit or traffic-way where this touching occurs. If
colliding objects do not separate, there is no last contact.
LIQUID DEBRIS – Scattered liquids from a vehicle or its cargo; spatter, dribble,
puddle, runoff and soak-in.
MAXIMUM ENGAGEMENT – Greatest penetration of one body, such as a
vehicle, by another during a collision; instant of greatest force between colliding
objects; time and place of this occurrence; position of bodies with respect to each
other at this instant.
MECHANISM OF INJURY – The force or energy that causes traumatic injury.
MIDDLE ORDINATE – The perpendicular distance between an arc and is chord
at the middle of the chord.
NOMOGRAPH – A chart on which three or more scales are arranged so that a
straight line drawn through values on any two will cross the third at a
corresponding value; a graphic calculator.
OBTUSE ANGLE - An angle greater than 90° and less than 180°.
ON-SCENE INVESTIGATOR – The first responding officer to a traffic crash who
has been trained to preserve crucial evidence, to measure and photograph the
scene, to interview drivers and witnesses, to take enforcement action, and to file
reports.
OPPOSITE-DIRECTION COLLISION – A collision between two traffic units
moving in opposite directions on the same roadway. Sometimes called a headon-collision.
OVERDEFLECTED – A condition of a tire in which the pressure on the road is
grater at the edges of the tread than in the middle; an overloaded or under
inflated tire condition.
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OVERREACTION – A driver’s excessive reaction to a hazardous situation that
produces another, or additional, hazard. Overreaction is usually a matter of too
much steering at high speeds, and often results in a yaw.
OVERSTEER – A characteristic of a motor vehicle as loaded that results in a
tendency to swerve toward the inside of a curve, especially at high speed. Motor
vehicles with more weight on the rear wheels than on the front, and with too little
pressure in the rear tires are likely to oversteer.
PARTIAL IMPACT – An impact in which motion is continuous between the parts
of colliding objects which are in contact with each other; sideswipe.
PASSIVE DEVICES – Non-electronic traffic control devices, including signs,
markings, and other devices located at or in advance of crossing to indicate the
presence of a crossing.
PERCEPTION – The general process of detecting some object or situation and
comprehending its significance.
PERSPECTIVE GRID – A parallelogram of known size placed on a flat surface
so as to appear in a photograph as a basis for locating marks or points which
also show in the photograph of the surface.
PHOTOGRAMMETRY – The use of photographs in making maps.
PUDDLE – A wet area on the road or roadside where dribble accumulates after a
vehicle has come to rest. A puddle often marks the final position of a vehicle
after a collision.
REACTION – A person’s voluntary or involuntary response to a hazard or other
situation that has been perceived; the response to a sensory stimulus. Reactions
may be reflex, simple, complex, or discriminatory.
REACTION DISTANCE – The distance moved or traveled by a vehicle or other
traffic unit during reaction time.
REACTION TIME – The time required from perception to the start of vehicle
control for tactical or strategic operations.
REFERENCE LINE – A line, often the edge of a roadway, from which
measurements are made to locate spots, especially spots along a roadway.
REFERENCE POINT – A point from which measurements are made to locate
spots in an area; sometimes the intersect of two reference lines; RP. A reference
point is described in terms of its relation to permanent landmarks.
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REPORTING – Basic data collection to identify and classify a motor vehicle
traffic collision and the persons, property, and planned movements involved.
Only strictly factual information is wanted, no opinions.
ROAD – The part of a traffic-way which includes both the roadway, which is the
traveled part, and any shoulder alongside the roadway. Where there are
unmountable curbs, the road and roadway are the same. If there is a guardrail,
the road is considered to extend to the guardrail.
ROADWAY – The part of the road intended for vehicle travel. It does not include
paved or otherwise improved shoulders or what is sometimes called a berm or
breakdown lane.
RUN-OFF – Rivulets of liquid debris from a puddle area flowing downhill toward
soak-in at the edge of the pavement; frequently the source of tire prints after a
collision.
RUT – A depression in soft or loose material, such as snow or dirt, made by a
rolling tire.
SCAR – Any sign that the road, roadside, or fixed object has been damaged or
marred by a traffic collision.
SCENE – The location of a traffic collision while people and vehicles involved are
still there. Compare with site.
SCRAPE – A broad area of a hard surface covered with may scratches or
striations made by a sliding metal part without great pressure.
SCRATCH – A light and usually irregular scar made on a hard surface, such as
paving, by a sliding metal part without great pressure.
SCUFFMARK – A tire friction mark made by a tire that is both rotating and
slipping on a road or other surface.
SHOULDER – That portion of the road contiguous with the roadway for
accommodation of stopped vehicles, for emergency use, and for lateral support
of the roadway structure; bank. The line between the roadway and the shoulder
may be a painted edge line, a change in surface color or material, or a curb.
SIDEWALK – That portion of a street between the curb lines, or the lateral edge
lines of a roadway, and the adjacent property lines, intended for use by a
pedestrian.
SIMPLE REACTION – A preplanned reaction to an expected hazard or other
stimulus.
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SITE – The location of a traffic collision after vehicles and people involved have
gone. Compare with scene.
SITUATION HAZARD – A circumstance that more or less endangers a traffic unit
on a trip and which must be avoided to prevent a collision.
SKIDMARK – A friction mark on a pavement made by a tire that is sliding without
rotation.
SKIP SKID – A braking skid mark interrupted at frequent intervals; the skid mark
made by a bouncing wheel on which brakes keep the wheel from turning.
Compare with gap skid.
SLAVE FLASH – A supplementary photoflash placed at a distance from the
master flash to increase the illuminated field in a photograph and fired by a
photoelectric device actuated by light from the master flash.
SLOPE – Ground that has a natural incline, as the side of a hill. Inclination or
slant, especially downward or upward.
SOAK-IN – An area on the shoulder or roadside saturated with liquid debris
either at the end of run-off or as a puddle marking the rest position of a vehicle
after a collision.
SPATTER – The collection of marks on the road made by liquid from the vehicle
or its cargo squirted from containers on the vehicle by force or collision. Spatter
areas are irregular in shape and often consist of many spots.
STABLIZED COLLISION SITUATION – The condition prevailing after motion and
other action constituting the events of a collision have ceased and no further
harm will ensue unless a new series of events is initiated by some means.
START (Simple Triage and Rapid Treatment) system – A system used at the
scene of multiple casualty incidents to quickly assess and prioritize care
according to three conditions: breathing, circulation, and level of consciousness.
STRIATIONS – Narrow, light, parallel stripes or streaks usually made by friction
or abrasion on the roadway or on vehicle parts.
SUPEREVLEVATION – The degree to which the outside edge of a roadway is
higher than the inside edge at a specific point on a curve; the changes in
elevation per unit distance across the roadway from inside to outside edge; bank.
SWERVE – A slight deviation from a straight-ahead path.
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TACTIC – Actions taken by a traffic unit to avoid a hazardous situation; steering,
braking, accelerating, etc. to avoid a collision or other collision. Often called
evasive action.
TANGENT – A line that touches a curve at only one point and is perpendicular to
the radius at that point; a term used to describe a straight offset method.
TECHNICAL FOLLOW-UP – Collection of additional facts from any source and
organization and preliminary study of all available data relating to a collision.
TIRE FRICTION MARK – A tire mark made when a slipping or sliding tire rubs
the road or other surface; skid marks; yaw marks; acceleration scuffs and flat-tire
marks.
TIRE MARK – A mark made on a road or other surface by a tire on a vehicle; tire
friction mark, imprint.
TRACKWIDTH – The distance on the ground between the center of the tire tread
on one side of the vehicle to the center of the tire tread on the opposite side.
TRACKING – Marks made when tires roll through puddles, run-off, or spatter
and, becoming wet, leave tire prints on the pavement as they roll on.
TRAFFIC – Pedestrians, ridden or herded animals, vehicles, street cars, and
other conveyances either singly or together while using any highway for
purposes of travel.
TRAFFIC CRASH RECONSTRUCTIONIST – An individual who has been trained
to conduct an in-depth reconstruction of the causes, events, and results of
vehicle crashes, including computation of speeds, direction of travel, and angle of
collision on the basis of evidence collected by on-scene investigators and crash
scene specialists.
TRAFFIC UNIT – An element of traffic; a person using a traffic-way for travel or
transportation; vehicle; pedal cycle, pedestrian, etc.
TREAD – That part of a tire designed to come in contact with the ground.
TRIANGULATION – A method of locating a spot in an area by measurements
from two or more reference points, the locations of which are identified for future
reference. Compare with coordinates.
UNCONTROLLED FINAL POSITION – A final position reached by a traffic unit
after a collision without conscious human intervention.
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UNDERBODY DEBRIS – Debris consisting of mud, dust, rust, paint, snow, o
road tar loosened by collision from the underside of the vehicle body, fenders,
and other parts.
UNIFORM VEHICLE CODE – A specimen set of motor vehicle laws, designed
and advanced as a comprehensive guide or standard for state motor vehicle and
traffic laws.
VEHICLE IDENTIFICATION NUMBER (VIN) – The number assigned to the
vehicle by the manufacturer primarily for identification and registration purposes.
WHEEL BASE – The distance from the center of the front wheels to the center of
the rear wheels or, if there is a tandem axle, the distance to the midpoint
between the two tandem axles.
WITNESS – Any person other than a driver or passenger who was at the scene
of a collision while vehicles or people involved were still there.
YAW – A sideways movement of a vehicle in turning; movement of a vehicle in
another direction than that in which it is headed; sideways motion produced when
sideways inertia force exceeds traction force. Often the result of overreaction or
exceeding the critical speed. Sometimes revealed by tire marks on the roadway.
YAWMARK – A scuffmark made while a vehicle is yawing; the mark made on the
road by a rotating tire which is slipping in a direction parallel to the axle of the
wheel.
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APPENDIX B - Wisconsin 2008 Traffic Crash Figures11

587 persons were killed in Wisconsin motor vehicle traffic crashes. This is
an average of two lives lost each day on Wisconsin traffic arteries.
 46,637 persons were injured in 33,766 reported injury crashes and 542
fatal crashes.
 Of the 587 persons killed, 10% (52 pedestrians and 9 bicyclists) were not
drivers or passengers of motor vehicles. Fifteen percent (87) were
motorcycle drivers or motorcycle passengers.
 Of the 587 persons killed, 40% (234) died in alcohol-related crashes and
32% (187) died in speed-related crashes.
 Fifty-six percent of all crashes occurred off the state highway and
interstate systems, on county trunk highways and local roads.
 The total number of registered vehicles was 5,455,985.
 The total number of licensed drivers was 4,075,764.
 The fatality rate per 100 million miles of travel was 1.29, up from 1.24 in
2007.
 The 2008 Department of Transportation Field Observation Study on Seat
Belt use states that in July, 2008, 74.2% of passenger vehicle occupants
(front outboard) used their safety belts. (Front outboard refers to the driver
and the right front seat passenger.)12
11
Wisconsin Department of Transportation 2008 Wisconsin Traffic Crash Facts
12
Wisconsin Department of Transportation Field Observation of Safety Belt Use in Wisconsin (July 2008)
http://www.dot.wisconsin.gov/safety/motorist/crashfacts/docs/seatbeltuse.pdf
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Wisconsin’s Highway Safety Clock13
13
Wisconsin Department of Transportation 2006 Wisconsin Traffic Crash Facts
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APPENDIX C – SLIDE-TO-STOP SPEED ESTIMATES
The formula used in calculating speed from skid marks is
V2
S=30f
in which S
represents the skid distance in feet, V the speed in miles per hour, and f the
coefficient of friction. This formula may be rewritten without changing its value as
follows: V2 = 30 x S x f. What the investigator is concerned with is the speed.
Simply substitute known factors in the right hand side of the equation, perform
the multiplications, extract the square root, and you will get the minimum speed.
This can be very easily done in a matter of a few seconds at the crash scene,
which gives you a result close enough to guide you in the investigation. It is a
quick method of determining whether there was sufficient speed involved to
warrant further analysis.
Example:
An investigator measures 50 feet of skid marks on dry, level concrete. The driver
involved states he was going only 25 miles per hour. The quick method of
estimating initial minimum speed is V2 = 30 x 50 x 60, or 900. The square root of
900 is 30. Therefore, the minimum speed is 30 miles per hour. This can be
done very simply without a test skid by arbitrarily assessing a 60 percent
coefficient of friction.
The coefficient of friction can be determined a number of ways:




Test-skid the crash vehicle or a similar vehicle.
Slide a test tire (not the whole vehicle) to get a friction coefficient.
Use existing highway department skid numbers for the road in question.
Look up the friction coefficient in a table and apply the appropriate
adjustments to them for the case at hand.
The first three methods are used in advanced investigations or in reconstruction.
The last method may also be used in advanced investigations or in
reconstruction. You can also use the table to estimate the speed at the scene.
However, this will only give you an estimate. Enforcement action should not be
taken based on your estimates.
The table of coefficients of friction gives a range of friction coefficients for several
surface descriptions. The values given in the table are for passenger cars and
pickup trucks equipped with typical tires. They are not typical values seen for
heavy trucks. This table provides an average coefficient of friction figure for a car
or pickup truck on a flat, straight surface. This table is reproduced from the
Traffic Accident Reconstruction Manual, published by the Northwestern
University Center for Public Safety. See page 62-14.
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While you will be able to reasonably calculate initial speeds by using this formula,
presentation in court will probably require expert testimony, including explanation
of the various physical laws and mathematical formulas involved. The expert, for
example a reconstructionist, will rely on the information you give him from the atscene investigation to reach his conclusion. This information must be accurate,
understandable, and complete, for without this information skid-mark evidence
will be of little value. With proper measuring and recording of skid-mark
evidence, accurate minimum initial speeds can be computed.
In complicated cases where not all wheels slide, or where the skid marks are on
different types of surfaces, it will probably be up to the expert to determine if any
use can be made of the skid mark evidence. In these instances, however, it is
important to record the evidence so that the expert may decide to what extent it
is usable.
COEFFICIENTS OF FRICTION OF VARIOUS ROADWAY SURFACES
DRY
DESCRIPTION
OF
ROAD SURFACE
Less than
30 mph
WET
More than
30 mph
From
To
From
To
PORTLAND CEMENT
New, Sharp
Traveled
Traffic Polished
.80
.60
.55
1.20
.80
.75
.70
.60
.50
1.00
.75
.65
ASPHALT or TAR
New, Sharp
Traveled
Traffic Polished
Excess Tar
.80
.60
.55
.50
1.20
.80
.75
.60
.65
.55
.45
.35
GRAVEL
Packed, Oiled
Loose
.55
.40
.85
.70
CINDERS
Packed
.50
ROCK
Crushed
Less than
30 mph
From
More than
30 mph
To
From
To
.50
.45
.45
.80
.70
.65
.40
.45
.45
.75
.65
.60
1.00
.70
.65
.60
.50
.45
.45
.30
.80
.70
.65
.60
.45
.40
.40
.25
.75
.65
.60
.55
.50
.40
.80
.70
.40
.45
.80
.75
.40
.45
.60
.75
.70
.50
.70
.65
.75
.65
.75
.55
.75
.55
.75
.55
.75
.55
.75
ICE
Smooth
.10
.25
.07
.20
.05
.10
.05
.10
SNOW
Packed
Loose
.30
.10
.55
.25
.35
.10
.55
.20
.30
.30
.60
.60
.30
.30
.60
.60
Fricke, L. (1990) Traffic Accident Reconstruction. Northwestern University Center for Public Safety. p. 62-14.
(Figure B-1: This table lists coefficients of friction of various roadway
surfaces. This table is not intended for large, heavy trucks.)
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December 2009
REFERENCES
Daecher Consulting Group Inc. (n.d.) Accident Investigation: Getting Facts to Make
Decisions. Retrieved August 31, 2007, from
http://www.uma.org/ppt/AccidentInvestigation.ppt
NHTSA- National Center for Statistics and Analysis: Traffic Safety Facts; 2006
Wisconsin Department of Transportation, 2008 Wisconsin Traffic Crash Facts;
June 2009 retrieved June 28, 2009 from
http://www.dot.wisconsin.gov/drivers/drivers/traffic/crast/final.htm
Baker, J. Stannard and Fricke, Lynn B. The Traffic Accident Investigation
Manual, Ninth Edition 1986
Fricke, L. (1990) Traffic Accident Reconstruction. (First ed.) Northwestern
University Traffic Institute Center for Public Safety.
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December 2009