Learning Outcomes Introduce the Highway Safety Manual Define procedures and techniques Demonstrate use of Safety Performance Functions Crash Modification Factors Safety always comes first in everything we do ID: 757775
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HIGHWAY SAFETY MANUAL
Copyright © 2016 STC, UKSlide2
Learning Outcomes
Introduce the Highway Safety ManualDefine procedures and techniquesDemonstrate use of
Safety Performance Functions
Crash Modification FactorsSlide3
Safety always comes first
in everything we do!Slide4
Safety & Roadway Design
Each design assumes a safety levelSection 109, Title 23, USC
Need for balancing of safety, mobility, economic considerations, protection and enhancement of natural environment, and preservation of community values
Tradeoffs among design, cost, and safetySlide5
Decision Making Process
Environment
Costs
Society
Safety
Capacity
Right of WaySlide6
Basic Safety Questions?
How can I predict safety performance of geometric design features?How can I quantitatively calculate safety effects?
How can I justify decisions based on safety implications? Slide7
Highway Safety Manual Purpose
Resource for professionalsSafety knowledgeDecision making toolsSlide8
The HSM is…
Analysis toolEstimations of safety performance
Prediction of crashesSlide9
The HSM is NOT…
Best Practice guideWarrantsStandardsSlide10
HSM 2010Slide11
A Safe Roadway?
List what are the top three items that make a roadway safe
1
.
2.
3. Slide12
Safe Roadway?Slide13
Safety Levels
Nominal safetyMeasured as compliance to standards, warrants and guidelines
Yes/No
Substantive safety
Measured by crash frequency and severity
Continuous scaleSlide14
Nominal vs. Substantive Safety
Design Value
Crash RiskSlide15
HSM ToolsSlide16
Crash Prediction Uses
Program levelSegment prioritizationProject level
Project needs assessment
Communication with the public
Documentation
Tort DefenseSlide17
HSM Contents
Introduction, Human Factors, Fundamentals
Safety Management Process
Predictive Methods
Crash Modification FactorsSlide18
HSM Companion Software
HSM Part
Supporting Tool
Part B:
Roadway Safety Management Process
SafetyAnalyst
www.safetyanalyst.org
Part C: Predictive MethodsIHSDMwww.ihsdm.orgPart D: Crash Modification Factors
FHWA CRF/CMF Clearinghousewww.cmfclearinghouse.orgSlide19
Some More Questions
What is the number of crashes for a given scenario?2-lane rural road with 5,000 AADT
4-lane rural arterial divided arterial with 20,000 AADT
What will be the safety effect if we
Widen shoulder
Add a median
Add a left-turn laneSlide20
How HSM Works
Safety Performance Function(SPF): regression equationCrash Modification Factor (CMF): adjustment factors
Calibration Factor (C): local adjustment
SPF
CMF
C
Predicted
CrashesSlide21
Part C: Predictive Methods
(1/3)
Safety Performance Functions (SPFs)
Regression models
Predict expected crash frequency
Developed from data for a number of similar sites
Developed for specific site types and “base conditions”
SPFSlide22
SPF Development
Average Daily Traffic (ADT)
Crashes/Year
SPF Slide23
SPF Example: 2-Lane Rural Roads
N
spf rs
= AADT x L x 365 X 10
-6
x e
(-0.312)
(Eq. 10-6)Note: assumed crash type and severity distribution Slide24
Part C: Predictive Methods
(2/3)
Crash Modification Factors (CMFs)
Adjusts SPF predicted value
Accounts for differences between base and site specific conditions
CMFSlide25
Part C: Predictive Methods (3/3)
Local calibration factor (Cr)
Adjusts SPF from HSM to local conditions
Addresses local variations
CSlide26
HSM Prediction Models
Prediction models forHomogeneous highway segments Intersections
Segments based on homogeneous
Geometry
AADT rangesSlide27
Segments and IntersectionsSlide28
HSM Process
Segment Facility
Geometry, AADT
Define Data
Limits, Type, Time, Geometry, AADT
Predict Crashes
SPF
Adjust Crashes
CMF, CSlide29
Cross Sectional ElementsSlide30
Safety and Operational Effects
Lane Width
Shoulder Width
Sideslope
Clear Zone
Crashes Operations
Head-on Capacity
Wider is “better” Wider means “faster” Run-off-Road Capacity Wider is “better” Functionality Run-off-road (severity) Maintenance Flatter is better Flatter is better Run-off-road Horizontal sight (frequency and severity) distance