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Application of HSM Predictive Method and IHSDM to Design
Decision-Making AN ARIZONA CASE STUDY
Presented by: Kohinoor Kar, Ph.D., P.E., PTOE and Mark Poppe, P.E. - Arizona Department of TransportationTaylor Ehrick, EIT and Mike Colety, P.E., PTOE - Kimley-Horn and Associates, Inc.
HIGHWAY SAFETY MANUAL, FIRST EDITION
SUBSTANTIVE VS. NOMINAL
PROJECT LEVEL DECISION-MAKING
OUTLINE
» Interactive Highway Safety Design Model» Case Study – AZ State Route (SR) 264
• Existing Conditions• Proposed Alternatives• Results of Analysis• Economic Analysis• Segment Prioritization
» Lessons Learned
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
INTRODUCTION
» Interactive Highway Safety Design Model (IHSDM)• Developed by FHWA• 6 Evaluation Modules• The Crash Prediction Module is a direct
implementation of the Predictive Method−Highway Safety Manual (HSM) Part C−User-friendly interface−Standardized yet customizable output reports
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
IHSDM INTERFACE
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
IHSDM INTERFACE
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
CASE STUDY – SR 264EXISTING CONDITIONS
» Arizona Pilot Project• Arizona is a support
state for HSM implementation under NCHRP 17-50
• SR 264−Milepost 441 to 466
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
Ganado, AZ
Begin ProjectMP 441.19
End ProjectMP 465.74
CASE STUDY – SR 264EXISTING CONDITIONS
» Rural Minor Arterial » Navajo Nation, Arizona » Undivided Two-Lane,
Two-Way Road » 12-foot travel lanes » 0-1-foot shoulders » Intermittent right and left
turn lanes » Intermittent passing lanes
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
CASE STUDY – SR 264EXISTING CONDITIONS
» Project Constraints• Limited Right-of-Way
−Additional Right-of-Way cannot be obtained from Navajo Nation at this time
• Large Cross Culverts• Existing Steep Side Slopes
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
EXISTING TRAFFIC AND CRASH DATA
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
ALTERNATIVE ANALYSIS
» Analyzed following alternatives: • Widen to 5-foot shoulders • Widen to 8-foot shoulders • Improve superelevation per AASHTO
recommendations » Shoulder widening alternatives also
included: • Centerline and shoulder rumble strips • Flattening of side slopes • Installing guardrail
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
ALTERNATIVE ANALYSIS
» Predictive Method includes:• Safety Performance Function (SPF)
−Roadway geometry/characteristics and traffic conditions determine roadway’s base condition
• Crash Modification Factors (CMFs)−CMFs for 13 road elements are applied to SPF
to create site-specific function• Local Calibration Factor (C)
−Accounts for jurisdictional/regional variations in climate, driver population, etc.
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
ALTERNATIVE ANALYSIS
» Notable variations from base condition• Shoulder Width• Roadside Hazard
Rating• Centerline
Rumble Strips
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
ALTERNATIVE ANALYSIS
» 17 Curves within project limits• Existing superelevation rates
−Range from 1.4% to 2.1% less than the AASHTO Method 5 recommend value
» Evaluate crash reduction associated with improved superelevation rates• Full reconstruction• Differential overlay
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
EXPECTED CRASH RESULTS
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
EXPECTED CRASH RESULTS (CONT’D)
» Crash reduction benefit of wider shoulders has diminishing returns as shoulder width increases
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
REGION-SPECIFIC CRASH SEVERITY PROPORTIONS
» Default HSM crash severity proportions based on State of Washington data
» For SR 264, developed proportions using region-specific data:• Three rural two-lane, two-way state
highways located within Navajo Nation and Hopi Tribe lands
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
REGION-SPECIFIC CRASH SEVERITY PROPORTIONS
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
ECONOMIC ANALYSIS OF ALTERNATIVES
» Performed Benefit-Cost ratio analysis to compare alternatives
» Calculated annual average number of crashes using crash data and crash severity distribution
» Annual averages from IHSDM analysis X Crash Reduction Factor (CRF) = total reduction in crashes
» Total reduction X unit cost = annual expected benefit in dollars
» Calculated costs for each alternative and annualized costs
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
ECONOMIC ANALYSIS OF ALTERNATIVES (CONT’D)
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
ECONOMIC ANALYSIS OF ALTERNATIVES (CONT’D)
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
ECONOMIC ANALYSIS OF ALTERNATIVES (CONT’D)
» 8-foot shoulders provide greatest safety benefit with maximum cost
» 5-foot shoulders provide the greatest safety benefit per dollar spent
» Superelevation Improvement benefits are outweighed by costs
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
SEGMENT PRIORITIZATION
» Split project into two separate construction segments due to budget
» Prioritized each segment based on potential crash reduction
» SR 264 segment limits: • Segment I - MP 441.19 to MP 452.00 • Segment II - MP 452.00 to MP 465.74
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
EXPECTED CRASH RESULTS (CONT’D)
» Segment II has greater crash reduction» Construct Segment II prior to Segment I» Small percentage difference (2.9%) in
crash reduction – consider other factors
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
LESSONS LEARNED
» IHSDM provides user-friendly interface for implementing HSM Predictive Method
» IHSDM can be used to quantify safety benefits for various proposed improvements
Application of HSM and IHSDM to Design Decision-Making: An Arizona Case Study
THANK YOU
» Mark Poppe• [email protected]
» Kohinoor Kar• [email protected]
» Mike Colety• [email protected]
» Taylor Ehrick• [email protected]