Module 1.2
Road Safety – A Complex Filed
Unit 1
Module 1.2
The Nature of
Road Safety
Road Safety – A Complex Field
Learning Objective
Duration 35 Minutes
At the conclusion of this module, participants will be able to:
Describe road safety as a complex, multidisciplinary,
multimodal field devoted to the prevention and/or
mitigation of crashes, injuries, and fatalities.
The major topics include:
• The complex nature of road safety
• Safety disciplines
• 4 Es of road safety
• Road safety modes
• Crash prevention paradigm shift
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Protecting the public from roadway crashes and the related
injuries and fatalities involves solutions that address the issue
from multiple perspectives, involve multiple disciplines, and
affect many different types of road users. Historically, road
safety has developed over the last century with the
development of the automobile.
Crashes and fatalities increased as the automobile became
more popular and as vehicle-miles of travel increased. Road
safety, however, was not officially recognized at the national
level until 1966 when Congress passed the National Traffic
and Motor Vehicle Safety Act. The law authorized the federal
government to set and regulate standards for motor vehicles
and the roadway and, as such, much of the initial safety efforts
focused on the contributions of the roadway, the automobile,
and the driver with respect to crashes. Many of the solutions
were, therefore, related to roadway and vehicle engineering.
While the design and operation of the roadway is primarily an
engineering task, road safety is not exclusive to engineering.
Road safety professionals include anyone who has an
influence on the safety of road users including those in public
health, public safety, and many other disciplines. Each of these
disciplines is able to provide a unique perspective and each
has specific methods for addressing road safety. However, the
actions of one discipline or even each discipline alone will not
address road safety completely. It is the interaction and
collaboration among these professionals that will lead to
continued safety improvements.
The challenge in creating these interactions and collaborations
stems from the diverse backgrounds and perspectives of
individuals within each discipline. First, each discipline has its
respective goals and objectives. While improving safety is the
overall goal, there are several means to the end (e.g., through
the roadway, vehicle, or road user improvements). There are
also diverse training and education curriculums for each
specific discipline. This creates various skill sets, which can
benefit road safety, but also creates barriers among the
disciplines including terminology and mindsets.
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To add to the complexity, these various disciplines are often
represented at the local, regional, State, and Federal level. So,
not only is it a challenge to improve collaboration among the
various disciplines, but also a challenge to overcome the
barriers within the disciplines.
Since 1966, road safety has substantially improved. Vehicle
and roadway designs have improved over time and many
countermeasures have been implemented to improve safety.
Law enforcement and education have been used to change
driver behavior and human factors considerations have been
incorporated in roadway and vehicle designs to better suit
road users. In addition, significant advancements in the
medical field and emergency response have helped mitigate
the consequences of crashes. However, these improvements
have only been effective up to a certain point and crash-related
injuries and fatalities remain a significant issue.
Safety professionals have continued to work within their
disciplinary “silos” with little interaction. As the graphic
above shows individual silos for storing grain, the disciplines
have also worked within walled off areas. Also, the local,
state, and federal agencies have worked mostly at their
respective levels, with limited knowledge and information
sharing. Thus, more recent efforts have sought to examine
road safety from a coordinated approach, with solutions that
are directed at road users, vehicles, and the roadway
environment, and carried out by professionals in multiple
disciplines at various levels. The challenge is to enhance and
develop this coordination in the future to realize the full
potential of road safety initiatives.
Several approaches for addressing the safety of a roadway
exist, and no single approach will address the issue
completely. Road safety professionals typically recognize four
major categories for addressing road safety; engineering,
education, enforcement, and emergency response. These four
categories are commonly known as the 4 Es of road safety.
The 4 Es have typically been used either as measures to correct
existing road safety issues or as crash prevention strategies.
Let’s take a look at each of the 4 Es.
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Engineers address road safety issues related to the roadway,
roadside, and vehicle. It is the engineers’ obligation and
responsibility to ensure the transportation system, including
all modes of transportation, is designed to meet the
expectations and limitations of road users.
 Roadway design manuals are based on human and vehicle
performance. When roadway safety problems arise, often
several engineering and operations measures can be
implemented to improve the physical environment of the
roadway and overcome the human or vehicle limitations.
For example, when crashes at a particular location are
associated with dark and unlit roadway conditions, many
options exist for improving visibility and guidance through
pavement markings, signage, and lighting.
 The roadside is another area where engineering can lead to
significant safety benefits. Engineering improvements such
as paved shoulders and rumble strips may prevent vehicles
from leaving the roadway, but several opportunities exist
for improving the roadside. When vehicles leave the
roadway it is important to provide a forgiving roadside
environment. Roadside slopes and obstructions (e.g.,
drainage structures, trees, and utility poles) are specific
attributes of the roadside that fall within the realm of
 The engineer can also impact safety through the design of
the vehicle. Vehicle design can affect safety during all three
stages (i.e., pre-crash, crash, and post-crash). Pre-crash
countermeasures include anti-lock brakes, vehicle stability,
and collision warning devices. Safety enhancements that
mitigate the severity during a crash include safety belts,
airbags, and vehicle integrity. In-vehicle technologies that
automatically notify emergency response can mitigate the
post crash environment. Human behavior can be modified
through other means, particularly education and
The purpose of education in road safety is to change the
behavior of road users (i.e., reduce unsafe behaviors and
increase safe behaviors). Education can be a powerful tool for
improving road safety because the human element is listed as
the primary cause in over 60 percent of crashes and a
contributing factor in over 90 percent of crashes. Educational
campaigns can be used in conjunction with engineering and
enforcement measures or as a single countermeasure. As a
single measure, education can be used to improve driving
skills and knowledge of the rules of the road as well as to
increase general awareness about road safety.
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Education can take the form of instructor-led training or invehicle training. When education is used in conjunction with
engineering or enforcement, the educational aspect is typically
used to explain why the countermeasure (engineering or
enforcement) has been implemented and how road users
should respond. For example, red light cameras are related to
both engineering and enforcement; however, it is important to
explain the issue of red light running to the public and the
need for the cameras or it is likely that such a tactic will be met
with serious opposition. Educational campaigns can also be
targeted to address specific unsafe actions (e.g., driving under
the influence, texting while driving, and not wearing a safety
belt) or to address specific road user populations (e.g., teen
drivers, motorcyclists, and pedestrians).
Unfortunately, engineering and education do not completely
solve road safety issues. For example, the engineer can design
a roadway and post a specific speed limit while an educational
campaign explains the dangers of excessive speed. Despite
engineering and education, some drivers will choose to exceed
the posted speed limit. Hence, enforcement is needed to
modify the behavior of the road user. Speeding, driving
under the influence (DUI), and safety belt use are associated
with a relatively large proportion of the total crash-related
injuries and fatalities. In other countries such as Australia, a
high level of success has been attained in reducing crashrelated injuries and fatalities through enforcement of these
behaviors. The United States is slowly improving safety belt
use through educational and enforcement campaigns;
however, the use of automated enforcement techniques (e.g.,
red light running and speed detection cameras) has met with
opposition. The intensity of DUI campaigns in the United
States lags behind other developed countries.
Furthermore, to be effective, enforcement must result in
Often judges and prosecutors do not
understand the seriousness of the issue and fail to ensure
citations are followed by maximum penalties.
Once a crash has occurred, emergency responders are
responsible for rescuing victims from the crash, providing
primary care, and protecting other road users from further
harm. While emergency responders typically deal with postcrash issues, it is important for these professionals to establish
a well-conceived incident management plan before the crash
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occurs. Emergency responders include law enforcement,
traffic engineers, fire and rescue, and emergency medical
services; each with a specific purpose. In general, law
enforcement officers are in charge of investigating the crash
and controlling traffic with assistance from traffic engineers.
Fire and rescue are responsible for removing victims from the
vehicle, if necessary, and often provide primary care. In some
jurisdictions, emergency medical services are carried out
under a separate public agency or privately contracted
company. Emergency responders often rely on assistance
from others including transportation agencies, towing and
recovery services, hazardous materials contractors, and traffic
reporting media. Through effective incident management,
these professionals can work in collaboration to mitigate the
consequences of crashes for those involved and reduce the
potential for further harm and traffic delay.
Historically, the 4 Es have been used as a means to address
crashes and the related injuries and fatalities. Over the years,
awareness of the 4 Es has increased, and they are now
commonly referenced in literature related to road safety
countermeasures. One positive result has been the increased
recognition that several different disciplines can contribute to
road safety. However, these disciplines have often confined
their prevention efforts to activities that relate centrally to
their core competencies, and have neglected to work together.
In essence, division of prevention efforts has created a silo
effect. It is time to move away from the traditional line of
thinking regarding the 4 Es (i.e., four separate and distinct
disciplines for addressing safety) and time to start thinking of
this as a method for addressing safety through partnerships
across the four disciplines.
Beyond the 4 Es of safety, other disciplines are also critical for
improving road safety including public health, human factors
and biomechanics, public and private administration, and
transportation planning.
Public health professionals deal with issues that affect the
general well being of society (i.e., morbidity and mortality).
As roadway-related crashes are the leading cause of
unintentional injuries and the sixth leading cause of death in
the United States, road safety is a major public health concern.
Public health officials have various opportunities to influence
road safety. In 2004, road safety was the theme of the annual
World Health Day celebration. This worldwide recognition of
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road safety included events of various forms, ranging from
new legislation, to hosting conferences and seminars, and
conducting high profile advocacy events for the general
Human factors and biomechanics professionals study the
capabilities and limitations of the human body, often in
relation to the design of various devices and systems. Within
the transportation field, the human factors and biomechanical
elements are critical to the safe design of the vehicle as well as
the safe design and operations of the roadway. Biomechanics
help explain the physical durability and limitations of the
human body.
Examples of human factors that affect road safety include the
physical strength required to depress the accelerator or brake
pedal, reaction time, visual acuity, and the affect of age on
these characteristics. Driver vision and reaction time influence
the total distance required to stop a vehicle, which is a critical
factor in the design of horizontal and vertical curves as well as
signal timing. Height, weight, and physical durability are all
factors related to the design of airbags and the required force
of deployment. If roadway and vehicle designs do not
consider the human element, the system could easily exceed
the limitations of the human body.
Public and private administrators affect road safety in a
variety of ways.
In the private sector, loss control administrators analyze
insurance claims to help set rates for vehicle and health
insurance. Public administrators develop and enforce policies,
procedures, and regulations to ensure the safe design and
operation of vehicles and roadway systems.
Transportation planners are involved with all modes of
transportation and, as such, can significantly influence safety.
Planners assess the need for various facilities, identify and
evaluate alternatives, and develop implementation plans.
However, the traditional planning process has considered
economic development, environmental quality, and mobility
and accessibility as the three primary concerns when
evaluating alternatives. Safety is often assumed to be a part of
improvements within these areas rather than a priority on its
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own. Planners have the opportunity to consider safety directly
in the evaluation of alternatives, and thus, an opportunity to
significantly impact road safety. More details on the
transportation planning purpose, process, and potential safety
impact are addressed in Unit 5.
Beyond the various disciplines involved in road safety, we
need to consider the various modes of travel as well. The
multimodal aspect of transportation and interaction among
the various modes adds to the complexity of road safety. The
modes of transportation include passenger vehicles,
motorcycles, pedestrians, bicycles, commercial vehicles, and
However, the design of vehicles and facilities is often focused
on a specific mode with little or no consideration for its
interaction with other modes. It is important to realize the
limiting factors and issues associated with the various modes
and how they affect the overall safety of the facility. Each
mode is discussed below in further detail with specific
emphasis on the interaction between modes and how the
interaction affects safety.
The most popular mode of transportation is the passenger
vehicle (e.g., cars, SUVs, vans, and light trucks) when
considering total miles traveled. As such, the design of
transportation facilities has reflected the desired use of the
automobile. However, the passenger car is also represented in
the largest percentage of crashes. In 2005, more than 94
percent of the 11 million vehicles involved in motor vehicle
crashes were passenger cars (NHTSA, 2006).
Often little attention is paid to the connectivity of other modes
when designing facilities for the automobile. While all trips
begin and end with some form of pedestrian activity, the auto
is the primary consideration, and several examples exist where
the auto has been the primary consideration, with little regard
for pedestrians. One example is parking lots. Numerous
parking lots are constructed with no sidewalks or designated
areas for pedestrians traveling to and from their vehicles.
Other safety considerations regarding the automobile include
the size and performance characteristics of the various types of
personal vehicles. Certain types of automobiles may be more
likely to be involved in specific crash types. For example,
when considering specific vehicle types involved in crashes,
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SUVs have the greatest percentage of rollover crashes
compared to all other vehicle types. This is noteworthy
because the proportion of vehicles that rolled over in fatal
crashes (21.1 percent) was four times higher than the
proportion in injury crashes (5.3 percent) and 16 times higher
than the proportion in property damage only crashes (1.3
percent) (NHTSA, 2006). Potential hazards are associated with
the diversity in the vehicle fleet. Vehicles range in height and
weight, which can influence the crash severity (e.g., small car
hits small car versus large truck hits small car). These are all
issues associated with road safety, and they must be
understood before noteworthy safety improvements can be
The interaction between commercial vehicles and other road
users, particularly passenger vehicles, can also create safety
concerns. The relative size of commercial vehicles creates
difficulties related to safety including blind spots, vehicle
control, and stopping distance. Roadways are often designed
based on the performance of passenger vehicles, rather than
larger commercial vehicles. In 2005, large trucks accounted for
eight percent of vehicles in fatal crashes, but only three and
five percent of vehicles involved in injury and property
damage crashes, respectively (NHTSA, 2006).
While passenger vehicles are represented in the greatest
percentage of crashes, other motorized vehicles are
represented in the greatest percentage of severe crashes when
adjusting for vehicles miles traveled and number of registered
vehicles. After adjusting for total vehicle-miles traveled and
number of registered vehicles, Table 1 on the next slide shows
the percentage of motorcycles and large trucks involved in
fatal crashes compared to passenger cars and light trucks.
Considering the total vehicle miles traveled and number of
registered vehicles, large trucks, and motorcycles are overrepresented in fatal crashes when compared to passenger cars
and light trucks. The passenger car, however, tends to be overrepresented in crashes resulting in injury or property damage.
In other words, when large trucks or motorcycles are involved
in crashes, the outcome is often severe.
Transit creates safety issues similar to large trucks when
considering the relative vehicle size. However, other distinct
safety considerations are associated with transit. Transit serves
as a form of mass transportation and, as such, transit facilities
need to accommodate pedestrians, particularly those with
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disabilities. While transit serves the pedestrian and bike
community, it often operates on the same facilities as other
motorized vehicles, which can create significant safety issues.
Transit stops are often located along commuter routes or other
routes with popular destinations. However, the placement of
the stop along the route can affect safety. It is desirable to have
the transit vehicle exit the traffic flow and stop in a designated
area; however, this can lead to issues when the vehicle enters
back into the traffic stream. If the transit vehicle must stop in
traffic, it is desirable to locate the transit stop where adequate
stopping sight distance is available for motorists approaching
from behind. These are just a few of the many examples of
safety concerns related to transit.
This slide clearly shows passenger vehicles are involved in
many more fatal and injury crashes than other types of
vehicles. However, controlling for vehicle miles of travel and
number of registered vehicles, passenger vehicles are the least
likely to be involved in serious crashes. Does this mean that
passenger vehicles are “safer” than other types of vehicles?
Not necessarily. We have to consider who is driving; where
they are driving; and break the data down much further to
answer this question. For example, the fatal and injury rate for
large trucks is higher than passenger vehicles; however, it is
generally not the truck occupants who are injured or killed but
rather the passenger vehicle occupants.
Pedestrian and bicycle fatalities are significant issues related to
overall road safety. While the total number of pedestrian- and
bicycle-related crashes is of concern, the severity of these
crashes is of greater concern.
In 2006, 4,784 pedestrians and 773 cyclists were killed in traffic
crashes in the United States (NHTSA, 2006). In addition,
61,000 pedestrians and 44,000 cyclists were injured in traffic
crashes in 2006 (NHTSA, 2006). Pedestrians and bicyclists are
the most vulnerable of the road users, but all too often they are
not considered in the design of roadway facilities. Higher
type facilities (e.g., Interstates and freeways) are not designed
to facilitate pedestrian and bicycle travel because their
primary purpose is high-speed movement of motorized
vehicles. However, several other functional classifications
should provide for pedestrian and bicycle mobility. One
example of inattention to pedestrian safety issues is the lack of
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connectivity of sidewalks, which creates “sidewalks to no
This section discussed the various modes of transportation
and the interactions that occur among modes. Examples were
provided to illustrate the interaction among various modes
and how these interactions affect safety. It is important to
understand and address the multimodal aspect of
transportation; otherwise, the overall safety of the facility is
As discussed in the previous sections, road safety is
multimodal and multidisciplinary in nature. Not only does
this create a complex environment, it also has fostered single
disciplinary and modal perspectives. It is often easier to
address safety issues related to a specific discipline or mode;
in part because that is how we have historically addressed
safety issues. However, the previous sections explain that
safety issues are often not related to a single mode or
The road safety profession, and the general public for that
matter, needs a paradigm shift. We need to move away from
the traditional approach to road safety (i.e., addressing safety
issues from a single disciplinary or modal perspective) to one
that addresses road safety with a coordinated, interdisciplinary, multi-modal, and systems perspective. While
crash and fatality rates continue to decline as vehicle-miles
traveled increases, the total number of fatal crashes has leveled
over the past decade. Many of the single modal and
disciplinary countermeasures have been implemented, (i.e.,
the “low hanging fruit” has been picked). Further reductions
in crashes and related injuries and fatalities will come from
interventions where disciplines work together to address road
safety across all modes and disciplines.
Consideration of several modes of transportation as well as
the collaboration among various disciplines has led to
successful crash prevention and safety improvements. The
following examples illustrate the benefits of interdisciplinary
relationships and multimodal considerations.
Many crash types and situations are more effectively
addressed through multidisciplinary collaboration. We will
consider two areas to demonstrate the more effective
approach: young drivers and safety corridors.
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Alcohol-related traffic crashes are a prevalent problem in the
US, especially among young males. A research study was
undertaken to understand issues and concerns surrounding
underage drinking and driving and to identify an effective
The first safety issue noted with teen driving is teens are
involved in nighttime crashes at significantly higher rates (per
100 million miles driven) than all other age groups.
The researchers also noted that the age when a teen learns to
drive effects their crash risk, with younger drivers posing
greater risk than drivers who are licensed even one year later.
The table shows that drivers learning at age 14 and licensed at
14 to 15 have significantly higher crash risks. Conversely,
drivers learning at age 16 and licensed between 16 and 17 have
the lowest crash risk.
The researchers examined the available evidence and devised
a solution that involves a multi-disciplinary effort using a twopronged approach to reduce underage drinking and driving.
The two effective strategies found to reduce impaired youth
driving include:
“Zero-Tolerance” laws prohibiting drivers under 21
from driving with even small amounts of alcohol in
their systems. Allowable blood alcohol content is from
0.00 to 0.02.
Graduated licensing systems that ease young people
into full driving privileges more gradually and
prohibit unsupervised night driving from 90 days to 6
These two programs are typically operated by different
agencies, once passed by the legislature. Typically the zerotolerance law is implemented by law enforcement agencies,
whereas driver licensing is administered by the department of
motor vehicles. Taken together, these programs illustrate that
a multi-disciplinary approach to addressing traffic safety
issues may be more powerful than individual programs.
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These programs are even more effective with parental
participation where parents enforce the laws themselves and
with full scale education programs to inform both parents and
novice drivers as to what the law is and why it is important to
abide by it. The education program may be undertaken by the
SHSO, the Department of Health, or some other agency
working in conjunction with law enforcement and the
licensing agency.
By 2006 most states had passed a graduated driver licensing
law although the elements of the laws vary greatly. One
analysis concluded that the strongest GDLs result in a 38%
reduction in fatal crashes and a 40% reduction in injury
crashes among 16 year old drivers. Even the weakest laws
resulted in fatal and injury crash reductions although to a
lesser extent.
The Insurance Institute for Highway Safety studied and rated
all the state laws. The map shows states with good, fair,
marginal, and poor laws. You can find out more about their
there, you can click on any state for the IIHS analysis.
Question: Where does your state fall in the rating scheme?
Answer: If anything less than good, you might find out what
elements are missing from your state’s law and begin to
educate your colleagues and officials on the effectiveness of
the missing elements.
Some states have legislative permission to identify “Safety
Corridors” which are high crash road segments in need of
attention. In these cases, the legislature directs the DOT to
identify corridors where the crash experience is higher than
average for all roads with similar characteristics, e.g.
Interstate, freeways, etc. The DOT places signs along these
corridors announcing to the public that the road segment has
been designated as a Safety Corridor and fines for speeding
are doubled. In addition, the state police or local law
enforcement increases enforcement in these areas. In some
cases, local advocacy groups are engaged to educate the public
about the dangers associated with the road segments and high
risk driving behavior, e.g., speeding and impaired driving.
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Finally, the state or local transportation authority may conduct
a RSA and make improvements to the infrastructure, e.g.
upgrade the guardrails, install cable median barrier, etc.
For example, the legislature directed the New Mexico
Department of Transportation (NMDOT) to identify
hazardous road segments and implement a safety corridor
program. NMDOT designated 12 safety corridors (two in each
district) to reduce speeds and serious crashes. The first step in
corridor selection was to identify the 10 segments of roadway
in each District with the highest number of serious crashes.
The lists were prioritized according to crash severity. NMDOT
met with local law enforcement and NMDOT District
personnel to discuss current projects on those segments. If
construction work was currently being implemented or if
there was no safe place for law enforcement to stop vehicles
and issue citations, the segment was deleted from the list. The
remaining top two locations in each District were selected for
implementation. A map of the corridors is available at:
By the beginning of 2008, crashes were reduced in all corridors
except one where the amount of traffic had increased
significantly. NMDOT coordinates crash data analysis with
the Districts; reviews existing law enforcement and
engineering initiatives; conducts public awareness campaigns
to elicit local support; installs signs designating the safety
corridors; and provides support to local law enforcement to
increase traffic law enforcement.
This case study shows how multidisciplinary approaches can
work effectively to save lives and reduce injuries. These
programs are not easily replicated because of the need for
legislation and the complexity involved when state and local
agencies must work together. Identifying the sites can also be
problematic. The DOT must be able to justify the designations
using crash data analysis and exposure metrics to differentiate
the safety corridors from other roadway segments. Often the
data are not available to conduct the analyses. Even when the
corridors can be identified, it may not be possible to
implement the campaign because construction work is
underway or enforcement activity is impractical due to the
volume of traffic or the lack of safe pullover places along the
Finally, the different disciplines, e.g., law
enforcement, engineering, emergency response, advocacy
groups, and others have different structures, missions, and
methods for conducting their business. Connecting the
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agencies to work hand in hand together requires good
communication and persuasion skills.
Road safety is a major health and economic issue. Protecting
the public from roadway crashes and the related injuries and
fatalities involves solutions that can address the issue from
multiple perspectives, involves multiple disciplines, and
affects many different types of road users and modes.
While interdisciplinary efforts are necessary to improve road
safety, the interaction among disciplines is often difficult to
achieve due to diversity in backgrounds, perspective,
education, and goals and objectives. Further, various levels of
government are often involved within a discipline. Therefore,
barriers must be overcome within and among the various
disciplines to further improve road safety.
Within the various disciplines, the four primary areas for
addressing road safety include engineering, education,
enforcement, and emergency response. These four areas are
known as the 4 Es. While recognition of the 4 Es has helped
emphasize the multidisciplinary nature of road safety, the
various disciplines often consider singular actions.
Collaborative efforts among the various disciplines have been
neglected in most situations.
Road safety includes all modes of transportation (e.g.,
passenger vehicles, motorcycles, pedestrians, bicycles,
commercial motor vehicles, and transit). The personal
automobile accounts for the greatest miles of travel and
greatest percentage of crashes. However, motorcycles and
large trucks are over-represented in fatal crashes after
adjusting for total vehicle miles and number of registered
vehicles. Also, specific safety concerns are related to the
interaction among the diverse vehicle types and modes of
transportation. Vehicles range in height, length, and weight,
create specific safety issues. Pedestrians and bicyclists are the
most vulnerable road users because they are completely
unprotected and move at different speeds than motorized
vehicles; each of these factors influences safety. It is important
to realize the limiting factors and issues associated with the
various modes and how they affect the overall safety of the
While it is often easier to consider safety within a specific
discipline or mode, it is important to move toward
multimodal and multidisciplinary actions.
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