NCHRP Project 17-45

Enhanced Safety Prediction Methodology and Analysis Tool for Freeways and Interchanges James A. Bonneson August 2012

Transportation Institute

Project Objectives

• Objectives – Develop safety prediction methodology • Freeways • Interchanges – Develop a software tool that implements the methodology – Document in a chapter for a future HSM

• • •

Project Oversight

NCHRP – Chuck Niessner, Mark Bush TRB – Rick Pain Panel – John Milton, Chair, Washington DOT – James Allen, FHWA, Region 2 – Geni Bahar, NAVIGATS Inc.

– Michael Matzke, FHWA, Office of Infrastructure – Johnson Owusu-Amoako, Maryland DOT – Dan Turner, Univ. of Alabama – Clayton Chen, FHWA, Office of Safety R&D

Research Team

• • Texas Transportation Institute – J. Bonneson , S. Geedipally, D. Lord, M. Pratt CH2M-Hill – J. Moller, T. Neuman

Project Status

• • Schedule – Begin: May 2009 – End: August 2012 Status – Final report and products submitted

Overview

• • • • • Background From System to Sites (Segmentation Process) Freeway Predictive Method – Freeway segments – Freeway speed-change lanes Ramp Predictive Method – Ramp and C-D road segments – Crossroad ramp terminals Method Scope

HSM Safety Evaluation Coverage

• • • 2010 HSM Part C Predictive Methods (52%) – Rural Two-Lane Highways (VMT: 362, 088 mvm) – Rural Multilane Highways (VMT: 356,810 mvm) – Urban and Suburban Arterials (VMT: 831,710 mvm) NCHRP Project 17-45: Freeways (33%) – Freeways (VMT: 963,805 mvm) – Ramps HSM Coverage (85%) – U.S. Streets and Highways (VMT: 2,966,506 mvm)

Freeway Safety Indicators

• Freeway Fatal Crash Rate – Fatality Analysis Reporting System (NHTSA) – U.S. highway system: 1.02 fatal cr/100 mvm 0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

2007 Rural Freeways Urban Freeways 2008 2009

Year

2010

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Freeway Segmentation Process

Concept – – Disaggregate road system into individual “sites” Rules for identifying segments and intersections Application – 3 freeway segments – – 5 C-D road segments 5 ramp segments

PLAN VIEW

– – 2 speed-change lanes 1 crossroad ramp terminal R ex4 Ramp Entrance Length, L en R en1 R ex5 R en2 R ex3 Ramp Exit Length, L ex CD 1 CD 2 CD 3 CD 5 CD 4 Fr 2 Fr 3 Fr 1

Freeway Predictive Method

• • Safety Performance Functions (SPFs) – Lanes: 4, 6, 8, 10 (9, 10 urban areas only) – Guidance for segments with 5, 7, 9 lanes Crash Modification Factors (CMFs) – Horizontal curve (one roadbed, both roadbeds) – Lane width – Inside shoulder width – Median width

Freeway Predictive Method

• CMFs – Median barrier (continuous and pieces) – High volume (portion of vehicles in congestion) – Lane change (weaving) – Outside shoulder width – Shoulder rumble strip – Outside clearance (clear zone width) – Outside barrier (continuous and pieces)

Ramp Segment Predictive Method

• • Segment SPFs – Lanes: 1, 2 (2 urban areas only) – Ramps, C-D Roads CMFs – Horizontal curve – Lane width – Right shoulder width – Left shoulder width

Ramp Segment Predictive Method

• • CMFs – Right side barrier – Left side barrier – Lane add, lane drop – Ramp speed-change lane – Weaving section (C-D road only) Supplemental Models – Ramp curve speed prediction model

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Ramp Terminal Predictive Method

SPFs – 7 configurations – Stop control, signal control Ramp Diagonal, Exit Diagonal, Entrance

Type: D3en

Crossroad

Type: D3ex

Ramp Diagonal, 4-Leg Ramp

Type: D4

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Ramp Terminal Predictive Method

SPFs – 7 configurations – Stop control, signal control 4-quad Parclo A Ramp 4-quad Parclo B Ramp 2-quad Parclo A Ramp Ramp

Type: A4 Type: A2

2-quad Parclo B

Type: B2

Ramp

Type: B4

Ramp

Ramp Terminal Predictive Method

• CMFs – Exit ramp capacity (ramp lanes and control mode) – Crossroad left-turn lane or bay – Crossroad right-turn lane or bay – Access point frequency (driveway count) – Segment length (distance to next intersection) – Median width

Ramp Terminal Predictive Method

• • CMFs for Signal-Controlled Terminals – Protected-only left-turn operation – Channelized right turn on crossroad – Channelized right turn on exit ramp – Non-ramp public street leg CMFs for One-Way Stop-Controlled Terminals – Skew angle

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Method Scope

Methods Do Not Address the Following – Ramp meters – HOV by-pass lanes on ramps – Frontage road segments or terminals – Freeways with buffer-separated HOV/HOT lanes • Note: can evaluate general-purpose lanes with barrier separation Buffer Barrier (ok)

• • •

Method Scope

Freeway Evaluation Scenarios – Interchange ramp spacing – Weaving section length – Reallocation of cross section width Interchange Scenarios – System interchange configuration – Service interchange configuration (parclo, diamond) Analysis Scale – Single year analysis or design life analysis – Freeway system analysis or individual section

Project Deliverables

• Draft final report – Main body: documents development of methods – Appendix: Draft HSM Freeways Chapter – Appendix: Draft HSM Ramps Chapter – Appendix: Draft HSM Appendix A for Part C – Appendix: Draft algorithm description

Project Deliverables

• • Enhanced Interchange Safety Analysis Tool (ISATe) – Excel spreadsheet – User manual ISATe Workshop Training Materials – PowerPoint slides – Course notes – Instructor guide

Questions – Comments?

• Implementation Activity – FHWA is implementing the predictive methods in the Interactive Highway Safety Design Model (IHSDM)