Application of HSM Predictive Method and IHSDM to Design ...

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


IHSDM INTERFACE


IHSDM INTERFACE


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


Ganado, AZ

Begin ProjectMP 441.19

End ProjectMP 465.74


» 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



» 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


EXISTING TRAFFIC AND CRASH DATA


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



» 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.



» Notable variations from base condition• Shoulder Width• Roadside Hazard

Rating• Centerline

Rumble Strips



» 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


EXPECTED CRASH RESULTS


EXPECTED CRASH RESULTS (CONT’D)

» Crash reduction benefit of wider shoulders has diminishing returns as shoulder width increases


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


REGION-SPECIFIC CRASH SEVERITY PROPORTIONS


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


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


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


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


LESSONS LEARNED

» IHSDM provides user-friendly interface for implementing HSM Predictive Method

» IHSDM can be used to quantify safety benefits for various proposed improvements


THANK YOU

» Mark Poppe• [email protected]

» Kohinoor Kar• [email protected]

» Mike Colety• [email protected]

» Taylor Ehrick• [email protected]

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