HSM: Another Tool for Safety
Management in Wyoming
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Acronym Soup
• WYDOT – Wyoming
Department of Transportation
• HSM – Highway Safety
Manual
• ITE – Institute of Traffic
Engineers
• SMS – Safety Management
System
• CARE – Critical Analysis
Reporting Environment
• CMF – Crash Modification
Factor (AMF in HSM)
• B/C – Benefit-Cost Ratio
• NPV – Net Present Value
• SPF – Safety Performance
Function
• RTM – Regression-to-the-mean
• ARF – Accident Reduction
Factor (CRF in HSM)
• AADT – Annual Average Daily
Traffic
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Early Stages
• Started before the Highway Safety Manual
was finally approved or published
• Highway Safety, Traffic, Road Design, and
District Operations people did attend a oneday introductory training at an ITE meeting
in May, 2010
• Plan is to incorporate the quantitative
processes into WYDOT’s Safety
Management System
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The WYDOT SMS Process
Pavement Project
Recommendations
Effectiveness
Studies
Theme Studies
Feedback Loop
District Inputs
Bridge Project
Recommendations
Safety Issue
Identification /
quantification
Safety
Project
Definition
Safety
Project
Prioritization
Project
Planning
Project
Deployment
CARE
Intersection Magic
Safety Analyst
Etc.
Network
Safety Index
• For all Safety work
• Done in advance
Includes all
Safety Projects
STIP, etc.
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Highway Safety Manual
• Crash modification factors
• Project planning input
• Process to calibrate for state
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Where the HSM fits in to Project Definition
Safety Project Definition step
Select appropriate
remedy(ies)
Identify expected
improvements (CMF)
Calculate lifecycle
benefits (NPV)
Methods for estimating safety effectiveness
(of a remedy / set of remedies)
Needs for each
Part C – Predictive Method (with
calibrated SPF, HSM CMFs)
Appropriate SPF, calibration, multiple
data sets, and CMF (limited)
Un-calibrated SPF and CMFs
(HSM, Part D, others)
Appropriate SPF, multiple data sets,
and CMF
Observed crash frequency and
CMFs (HSM, Part D, others)
Historical crash data and CMF,
doesn’t address RTM
In decreasing order of reliability; from
HSM training (4.56)
Also, calculate lifecycle cost,
project B/C ratio
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Which Method to use?
• Use HSM Part C – Predictive Method
– Pros: Most reliable (according to HSM)
– Cons: Needs lots of data sets (WYDOT does not have
several); needs calibration (extensive process)
• Use un-calibrated SPF
– Pros: Still reliable (according to HSM)
– Cons: Needs lots of data sets (WYDOT does not have
several);
• Use observed (historic crashes)
– Pros: Needs least amount of additional data; familiar to
people (similar to previous use of ARF)
– Cons: Least reliable (according to HSM)
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Applying CMF – Using observed crash
frequency
Specific Site being analyzed
Observed crashes
Select
remedies
Identify CMF*
Expected change
in crash counts
Expected benefits
of remedy(ies)
* Generally studies refer to Crash / Accident
Reduction Factors which translate to CMF
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Calibrate
each SPF
Applying CMF – HSM Part C Predictive
Method
Determine C for each SPF
Select appropriate SPF
Determine SPF for site
(based on facility)
Determine volume for site
Adjust SPF
(based on site)
Expected average
crash frequency for the site
Identify site characteristics
(delta from baseline)
Up to 18 parameters
Select
Remedy(ies)
Engineering judgement
Find corresponding CMF
for the remedy(ies)
Apply CMF
From HSM lists
(Part C, Part D)
Difference =
expected benefits
of remedy(ies)
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HSM Part C – Expected average crash frequency
(example; 2-lane rural highway segment)
Expected change in
average crash frequency
for specific site given
selected remedies
=
AADT x Length + (365*10-6) x e-0.312
X
CMF(lw) X CMF(swt) X CMF(hc) X CMF(se) X CMF(gr) X CMF(dd) X CMF(crs) X CMF(pl) X CMF(2lt) X CMF(rd) X CMF(l) X CMF(ase)
X
1 - ( CMF1
X
CMF2 )
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HSM Core Data Needs for Segments
Factor
Unit
WYDOT Status
Length of segment
miles
OK
AADT
veh/day
OK1
Lane width
ft
OK
Shoulder width
ft
OK
Shoulder type
paved, gravel, etc.
OK
Length of horizontal curve
mi
OK
Radius of curvature
ft
OK
Spiral transition present
y/n
OK
Superelevation variance
ft/ft
Not yet
Grade
%
OK
Driveway density
driveways/mile
Working2
Centerline rumble strips present
y/n
Assume no
Passing lanes present
y/n
maps3??
Two-way left turn lanes present
y/n
maps3??
Roadside rating hazard
1-7 scale
maps4??
Segment lighting present
y/n
Assume no
Auto speed enforcement present
y/n
Assume no
Calibration factor
NOTES:
1.However, need
projected future traffic
volumes
2.Data identified as
coming from Pathways
log.
3.Roadway width will
catch many of these,
but not all. Should we
modify number of
lanes table for this?
4.DCE’s agreed to
gather this data in FY
2011, specifics to be
determined?
TBD
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Observations & Conclusions
• HSM Predictive method requires too much effort at this
point
– To obtain missing data sets, to perform SPF calibration
• HSM “Observed Crash Frequency” method can readily be
used in WYDOT’s SMS approach
– Easier to combine multiple remedies
– Decision needed regarding “expected” crash rates
• Not all WYDOT remedies are covered by HSM Part C
CMFs
– Can also use Part D CMFs but with caveats
• Need additional data
– Expected future traffic volumes (or at least growth rate)
• In order to calculate lifecycle crash reduction
– Roadside data
• In order to support some of the CMFs (e.g. way left turn lanes,
passing lanes, though partially available in the # lanes table)
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Going Forward
• Who should attend HSM training?
• Finalize the starting remedies to consider for now
• Identify appropriate CMF values to use for each remedy
– Work with District Traffic Engineers
– Document logic for selection of values
• DiExSys is continuing research (Highway Safety)
– Terrain (flat/rolling/mountainous) might be a sufficient surrogate
for roadside hazard rating
• Address need for future traffic volume data
• Other possibilities
– Prototype HSM calculation of expected average crash frequency
for different segments using available data sets
– Determine need/ability to get missing data sets
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