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Enhanced Safety Prediction Methodology and Analysis Tool for Freeways and Interchanges

NCHRP Project 17-45. Enhanced Safety Prediction Methodology and Analysis Tool for Freeways and Interchanges. James A. Bonneson August 2012. Project Objectives. Objectives Develop safety prediction methodology Freeways Interchanges Develop a software tool that implements the methodology

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Enhanced Safety Prediction Methodology and Analysis Tool for Freeways and Interchanges

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  1. NCHRP Project 17-45 Enhanced Safety Prediction Methodology and Analysis Tool for Freeways and Interchanges James A. Bonneson August 2012

  2. 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

  3. 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

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

  5. Project Status • Schedule • Begin: May 2009 • End: August 2012 • Status • Final report and products submitted

  6. 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

  7. 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)

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

  9. 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 • 2 speed-change lanes • 1 crossroad ramp terminal In

  10. 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

  11. 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)

  12. 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

  13. 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

  14. Ramp Terminal Predictive Method • SPFs • 7 configurations • Stop control, signal control Diagonal, Entrance Diagonal, Exit Diagonal, 4-Leg

  15. Ramp Terminal Predictive Method • SPFs • 7 configurations • Stop control, signal control 4-quad Parclo B 4-quad Parclo A 2-quad Parclo B 2-quad Parclo A

  16. 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

  17. 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

  18. 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 Barrier (ok) Buffer

  19. 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

  20. 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

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

  22. Questions – Comments? • Implementation Activity • FHWA is implementing the predictive methods in the Interactive Highway Safety Design Model (IHSDM)

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