1 / 38

LOW COST SAFETY IMPROVEMENTS

LOW COST SAFETY IMPROVEMENTS. The Tools – Identification of High Crash Locations – Session #2. Identification of High Crash Locations. Learning Outcomes: Identify appropriate Engineering Countermeasures by using the 6 Step Crash Mitigation Process. List of .

mandel
Télécharger la présentation

LOW COST SAFETY IMPROVEMENTS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. LOW COST SAFETY IMPROVEMENTS The Tools – Identification of High Crash Locations – Session #2

  2. Identification of High Crash Locations Learning Outcomes: • Identify appropriate Engineering Countermeasures by using the 6 Step Crash Mitigation Process

  3. List of Network Screening or Site Selection Sites for Review Document Detailed Engineering Study the Analysis Document Project Selection, the Implementation, & Evaluation Evaluation HSIP Planning

  4. Conventional Screening • Conventional techniques of screening use are known to have difficulties in identifying ‘unsafe’ sites: • Crash counts = bias to high volume sites • Crash rates = bias to low volume sites • Crash rates’ assumption of linearity is invalid • Regression-to-mean (RTM) effect if sufficient allowance is not made for random errors

  5. What is Network Screening? • Highway network system made up of segmentsand intersections • Network screening is a systematic examination of all entities • Purpose: To rank all entities, based on selected criteria, in order to conduct detailed safety studies http://www.ncdot.org//planning/statewide/gis/DataDist/CountyMap.html Money should go where it achieves the greatest effect in terms of preventing crashes and reducing their severity

  6. PSI Index Approach • New and different approach to identify the Potential for Safety Improvement (PSI) • Application of Safety Performance Functions (SPFs) for each crash severity class for different reference groups • PSI values for fatal, injury and PDO crashes combined = PSI Index • Weights (relative cost) are applied to PSI values

  7. PSI Index Screening • PSIIndex is estimated for each location • Locations are ranked in descending order of PSIIndex values • Locations with largest PSIIndex values have most potential for crash reduction

  8. SafetyAnalyst Tools • Network screening to identify sites with promise for safety improvement • Diagnosis of safety concerns • Selection of countermeasures • Economic appraisal of countermeasures • Priority ranking of countermeasures • Evaluation of implemented projects

  9. The six steps in the crash mitigation process • Identify Sites • Collect Crash Experience • Gather Field Conditions • Identify Contributing Factors and Countermeasures • Assess and Select Countermeasures • Implement and Evaluate

  10. Step 1: Identify Sites with Potential Safety Problems • Crash data • Traffic Measures • Field Observations • Complaints • Enforcement input • Surrogate measures

  11. Step 1: Identify Sites with Potential Safety Problems Crash Information Methods: • Total Number of Crashes • Crash Density (Crashes per mile) • Crash Rate (Crashes per million vehicle miles) • Number Quality Control • Rate Quality Control • Crash Severity • Severity Index • Crash Index

  12. Crash Rate Calculation Roadway Segment: CR = N / [ADT x 365 x L x 10-6] where CR is expressed as “Crashes per million vehicle miles (or kilometers)” and N = Number of crashes per year ADT = Average Daily Traffic L = Length of segment (mi or km)

  13. Crash Rate Calculation: Segment Example: For N = 50 crashes for 3 year period ADT = 3,000 Average Daily Traffic L = 2.8 miles CR = N / [ADT x 365 x L x 10-6] CR = 50 / [3,000 ADT x 3 yrs x 365 x 2.8 miles x 10-6] CR = 5.43 crashes per million vehicle miles

  14. Average Crash Rates

  15. Step 1: Identify Sites with Potential Safety Problems *From Mn DOT Traffic Safety Fundamentals Handbook

  16. Crash Rate Calculation Intersection: CR = N / {[Sum (ADT)s /2] x 365 x 10-6} where CR is expressed as “crashes per million entering vehicles” and N = Number of crashes per year Sum (ADT)s = Sum of all Average Daily Traffic entering the intersection

  17. Crash Rate Calculation: Intersection Example: For N = 25 crashes for 3 years ADT (N) = 10,000 ADT (S) = 9,000 ADT (E) = 3,500 ADT (W) = 4,000 Sum (ADT)s=(10,000+9,000+3,500+4,000) = 26,500 CR = N / {[Sum (ADT)s /2] x 365 x 10-6} CR = 25/ {26,500/2] x 3 yrs x365 x 10-6} CR = 1.72 crashes per million entering vehicles

  18. Collision Types at Rural Intersections

  19. Average Intersection Crash Rates • Average of 1.5 crashes per year for Un-Signalized Intersections in rural areas– recent California analysis* • Average of 2.5 crashes per year in urban areas *NCHRP 500, Volume 5: A Guide for Addressing Unsignalized Intersection Collisions, 2003.

  20. Severity Index Severity index (SI) is the ratio of crashes involving an injury or fatality to total crashes

  21. Step 2: Characterize the Crash Experience Prepare a Collision Diagram

  22. Non-Crash Based Procedures References- Appendix A:

  23. Step 3: Characterize Field Conditions

  24. Step 3: Characterize Field Conditions

  25. Step 4: Identify Contributing Factors and Appropriate Countermeasures *See Appendix for Tables 12, 13, 14 and 15

  26. Step 5: Assess Countermeasures and Select Most Appropriate Page 11-14 of Appendicies • See Appendix Tables 12, 13, & 14 for “Contributing Factors” Poor Delineation

  27. Step 5: Assess Countermeasures and Select Most Appropriate • go to Table of Crash Reduction Factors in the Appendicies, page 11-22, Warning Signs, 3rd row

  28. Step 6: Implement Countermeasures and Evaluate Effectiveness Improve Delineation - Advance Warning Sign for Curve with Advisory Speed Plaque CRF = 22%

  29. Step 3: Characterize Field Conditions Traffic Data Studies: • Traffic Volume – Turning Movement, ADT • Spot Speeds • Traffic Conflict Study • Sight Distance Evaluation

  30. Traffic Crash Costs: AIS Level Cost Per Injury SeverityDescriptor(Dollars) Property Damage Only 65,000 AIS 3 Serious Injury 175,000 AIS 4 Severe 565,000 AIS 5 Critical 2,290,000 AIS 6 Fatal 3,000,000

  31. Identification of High Crash Locations – Exercise III • For the Countermeasure Advance Curve Warning Signs + Advisory Speed Plaque = 22%; Calculate the benefit $$ for “before period” of 7 crashes Discussion

  32. Introduction – Exercise III • For the Countermeasure Advance Curve Warning Signs + Advisory Speed Plaque = 22% Discussion Benefit for “Before Period of 7 Crashes = 7 crashes x CRF of 22% = 7 x 0.22 = 1.54 crashes reduced Severity distribution = 0.32 (Inj+Fatal) + 0.68 Pdo Benefit = (1.54 x 0.32 x $565,000) + (1.54 x 0.68 x $65,000) = $345,100

  33. Identification of High Crash Locations Appendix H: Typical Benefit/Cost Ratios * From MN DOT Traffic Safety Fundamentals Handbook

  34. Identification of High Crash Locations Review Questions: • What are the six steps in the crash mitigation process?

  35. Review: What are the six steps in the crash mitigation process? • Identify Sites • Collect Crash Experience • Gather Field Conditions • Identify Contributing Factors and Countermeasures • Assess and Select Countermeasures • Implement and Evaluate

  36. Identification of High Crash Locations Review Questions: Lighting CRF = 50+% • What low cost safety measure has the highest benefit to cost ratio?

  37. Identification of High Crash Locations Learning Outcomes: • Identify appropriate Engineering Countermeasures by using the 6 Step Crash Mitigation Process

  38. Identification of High Crash Locations Questions?

More Related