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Overview of the New Highway Safety Manual

Overview of the New Highway Safety Manual. Karen Dixon, Oregon State University NCHRP 17-38 Project Member. June 16, 2009 Manchester, NH. AASHTO Subcommittee on Traffic Engineering. Presentation Summary. 1. 2. 3. 4. 5. Overview of the new HSM. I. WHAT IS THE HSM?. What is the HSM?.

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Overview of the New Highway Safety Manual

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  1. Overview of the New Highway Safety Manual Karen Dixon, Oregon State University NCHRP 17-38 Project Member June 16, 2009 Manchester, NH AASHTO Subcommittee on Traffic Engineering

  2. Presentation Summary 1 2 3 4 5

  3. Overview of the new HSM I. WHAT IS THE HSM?

  4. What is the HSM?

  5. The Vision of the HSM - A Document Akin To the HCM 1 2 3

  6. What the HSM is NOT vs • The HSM does not set requirements or mandates • The HSM isnot a best practice document for design or operations. • The HSM contains no warrants or standards and does not supersede other publications that do.

  7. The HSM does not establish a legal standard of care nor does it create a duty to the public.

  8. Overview of the new HSM II. Why Do We Need the HSM?

  9. Is This Road “Safe” or “Unsafe”? What does safety really mean?

  10. Highway Safety Has Two Dimensions Examined in reference to compliance with standards, warrants, guidelines and sanctioned design procedures The expected or actual crash frequency and severity for a highway or roadway *Ezra Hauer, ITE Traffic Safety Toolbox Introduction, 1999

  11. Unlike Nominal Safety, Substantive Safety is a Continuum Substantive Safety Nominal Safety CRASH RISK CRASH RISK DESIGN DIMENSION Lane Width, Radius of Curve, Stopping Sight Distance, etc. DESIGN DIMENSION Lane Width, Radius of Curve, Stopping Sight Distance, etc.

  12. Nominal Safety vs Substantive Safety Low Nominal High Substantive High Nominal High Substantive CRASH RISK Low Nominal Low Substantive High Nominal Low Substantive DESIGN DIMENSION Lane Width, Radius of Curve, Stopping Sight Distance, etc.

  13. Substantive Safety May Vary When Nominal Safety Does Not Alternative 1 Existing Conditions Alternative 3 Alternative 2

  14. We’re Interested in Other Impacts for Project Level Decisions – What About Substantive Safety? • Construction • Plans • Cost Models • Real estate • appraisals • DOT databases • HCM • CORSIM • PASSER • TRANSYT7F • VISSIM Design Criteria (nominal safety) • Traffic Noise Model 1.0 • CAL3QHC • Mobile 5a • 3-D Visualization • CITYGREEN The HSM More quantitative Greater weight Safety Environmental Traffic Right-of-Way Costs Impacts Impacts Operations

  15. The HSM Contains Best Science & Research • Synthesis of previous research • New research commissioned by AASHTO and FHWA

  16. Overview of the new HSM III. HOW WAS THE HSM DEVELOPED?

  17. The HSM – A Ten-year Research And Development Effort 1999 2000 2003 2007 2010 Future Research, research and more research

  18. Joint Subcommittee sponsored by 7 TRB committees Thousands of hours of volunteer effort Research program funded by NCHRP, AASHTO & FHWA Significant Effort & Professional Support Produced the HSM

  19. Research Path to the HSM v.1

  20. Overview of the new HSM IV. What is Covered by the HSM?

  21. Outline of the HSM

  22. PART AINTRODUCTION, HUMAN FACTORS, & FUNDAMENTALS

  23. Part BRoadway Safety Management Process Prioritization of Improvement Projects Countermeasure Selection Network Screening 6 7 9 5 8 4 Safety Effectiveness Evaluation Diagnosis Economic Appraisal

  24. Part CPredictive Method • Methodology • Applications • Safety issues not explicitly addressed by the methodology • Example problems • References • Calibration • Combining predicted with observed crashes Special Part C Common Procedures

  25. Definition of HSM Terms • Safety Performance Function (SPF) – a regression equation used for estimating the predicted crash frequency at a site for a given “base condition” • Accident Modification Factor (AMF) – used to adjust the “base condition” in the SPF to specific site characteristics • Calibration Factor (C) – adjusts average crash frequencies calculated from the SPF to local site conditions

  26. Predicting Crashes – Defining Roadway Segments and Intersections

  27. Crash Estimation Equation N predicted = N spf x C x AMF1 x AMF2 x … Calculate the Roadway Segment Npredicted and the Roadway Intersection Segment Npredicted separately

  28. Summation of Crashes

  29. HSM Regional SPF Calibration Step 1 – Identify facility types of interest Step 2 – Select sites for calibration of each facility type Step 3 – Obtain data for each facility type applicable to the calibration period Step 4 – Apply the appropriate Part C predictive model to estimate expected crash frequency for each site during the calibration period Step 5 – Compute calibration factors for use in Part C predictive model

  30. Calibration Step 1 – Facility Types

  31. Calibration Step 2 – Select Sites for Calibration of Facility Types • Each facility type will need a minimum of 30 to 50 sites. • Calibration sites should be based on road segments or intersections as shown in Step 1 • Total crashes observed at all sites unique to a specific facility type should be a minimum of 100 per year – this should not be investigated until after the sites are selected

  32. Calibration Step 3 – Obtain data for each Facility Type • Total observed crash frequency for a period selected (usually 1 to 3 years) • Site characteristic data complying with required versus desirable data elements as shown in the following slides

  33. Data Element Needs

  34. Data Element Needs (continued)

  35. Data Element Needs (continued)

  36. Calibration Step 4 – Apply Predictive Method • Apply the applicable HSM Part C predictive method to predict total crash frequency for each site during the calibration period

  37. Calibration Step 5 – Compute Calibration Factors • Create a proportional factor to apply to regional data as follows:

  38. What is the EmpericalBayes (EB) Method? • Tool to compensate for the potential bias due to regression-to-the-mean • Correct for unusual crash trends • Uses predicted crashes paired with observed crashes for a more reliable crash estimate

  39. Part DAccident Modification Factors

  40. Overview of the new HSM V. WHO SHOULD USE THE HSM?

  41. Who Should Use the HSM?

  42. Assess the system needs & identify projects/studies • Program projects • Evaluate system-wide safety effects of programs

  43. Define problem(s) and assist in scoping • Identify potential solutions • Assess or evaluate multiple alternatives and expected quantitative safety effects • Aid in identification of a preferred alternative

  44. Evaluate safety of alternative design approaches • Assist in review & documentation of design exceptions, variances and waivers • Inform decisions on construction staging, work approaches, etc.

  45. Monitor operations to maintain balance among safety, mobility and access. • Evaluate the effectiveness of implemented improvements

  46. Overview of the new HSM VI. When Will the HSM be Available?

  47. Implementation Schedule

  48. Training & Outreach Activities • Sept 2009 – Jan 2010 • Conduct two or three multi-state pilot courses • August 2009 • TRB Task Force Meeting • TRB 2010 Annual Meeting • One-day workshop • Training materials, including “Train-the-trainer” available upon HSM release

  49. Overview of the new HSM VII. Where Can One Find More Information About the HSM?

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