HSM: Another Tool for Safety Management in Wyoming

HSM: Another Tool for Safety Management in Wyoming

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Excellence in Transportation

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 one-day 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

Safety Issue Identification / quantification

Safety Project

Definition

Safety Project

Prioritization

Project Planning

Effectiveness Studies

ProjectDeployment

Prioritized opportunities

to analyze

Feedback Loop

Candidate S

afety Projects

Benefits and costs; B

/C

Projects consolidated

with other program

s

Prioritized safety

project stack

Updates to CMFs, Guidance

Deployed &

Operational

NetworkSafety Index

Pavement Project Recommendations

Bridge Project Recommendations

CAREIntersection MagicSafety AnalystEtc.

Includes all Safety Projects

• For all Safety work• Done in advance

STIP, etc.

Theme Studies

District Inputs

4Excellence in Transportation

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

Methods for estimating safety effectiveness (of a remedy / set of remedies)

Appropriate SPF, calibration, multiple data sets, and CMF (limited)

Select appropriateremedy(ies)

Identify expected improvements (CMF)

Calculate lifecycle benefits (NPV)

Part C – Predictive Method (with calibrated SPF, HSM CMFs)

Un-calibrated SPF and CMFs (HSM, Part D, others)

Observed crash frequency and CMFs (HSM, Part D, others)

Appropriate SPF, multiple data sets, and CMF

Historical crash data and CMF, doesn’t address RTM

In decreasing order of reliability; from HSM training (4.56)

Needs for each

Also, calculate lifecycle cost,project B/C ratio


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

Observed crashes

Specific Site being analyzed

Selectremedies

Expected changein crash counts

* Generally studies refer to Crash / Accident Reduction Factors which translate to CMF

Expected benefits of remedy(ies)

Identify CMF*


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Applying CMF – HSM Part C Predictive Method

Select appropriate SPF(based on facility)

Identify site characteristics(delta from baseline)

SelectRemedy(ies)

Apply CMF

Expected average crash frequency for the site

Difference = expected benefits

of remedy(ies)

Determine SPF for site

Find corresponding CMF for the remedy(ies)

Up to 18 parameters

From HSM lists(Part C, Part D)

Calibrateeach SPF

Determine C for each SPF

Determine volume for site(based on site)

Adjust SPF

Engineering judgement


HSM Part C – Expected average crash frequency(example; 2-lane rural highway segment)

CMF(lw) CMF(swt) CMF(hc) CMF(se) CMF(gr) CMF(dd) CMF(crs) CMF(pl) CMF(2lt) CMF(rd) CMF(l) CMF(ase)

Expected change in average crash frequency

for specific site given selected remedies

X

X X X X X X X X X X X

=

Adjust for la

ne width

Adjust for shoulder w

idth, type

… horizontal curve (3 factors)

… superelevation

… grade

… driveway density

… centerline rumble strip

s

… passing lanes

… roadside rating hazard

… lighting

… automatic speed

enforcement

… 2-way left turn lanes

SPF for rural 2-lane

AADT x Length + (365*10-6) x e-0.312

X

CMF1 CMF2X

… for selected

remedies

1 - ( )


HSM Core Data Needs for SegmentsFactor 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 TBD

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?


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)


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


Documents

HSM: Another Tool for Safety Management in Wyoming