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

2. Identification of High Crash Locations Learning Objectives:  Describe the HSIP Planning Process  Crash Mitigation Process  Identify appropriate Engineering Countermeasures from Crash Patterns

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

4. What is Network Screening?  Highway network system made up of segments and 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 Money should go where it achieves the greatest effect in terms of preventing crashes and reducing their severity http://www.ncdot.org//planning/statewide/gis/DataDist/CountyMap.html

5. Identification of High Crash Locations The six steps in the crash mitigation process

6. 1.Identify Sites 2.Collect Crash Experience 3.Gather Field Conditions 4.Identify Contributing Factors and Countermeasures 5.Assess and Select Countermeasures 6.Implement and Evaluate

7. Identification of High Crash Locations Step 1: Identify Sites with Potential Safety Problems Crash data Traffic Measures Field Observations Complaints Enforcement input Surrogate measures

8. Identification of High Crash Locations Step 1: Identify Sites with Potential Safety Problems Crash data  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

9. Most Common Reporting Errors  Crash location  Direction of travel  Driver action  Pedestrian condition  Vertical road characteristics

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

11. Identification of High Crash Locations 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)

12. Identification of High Crash Locations 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

13. Identification of High Crash Locations Different Hwy Types Experience Different Crash Rates

14. Identification of High Crash Locations Step 1: Identify Sites with Potential Safety Problems *From Mn DOT Traffic Safety Fundamentals Handbook

15. Identification of High Crash Locations Intersection: AR = N / {[Sum (ADT)s /2] x 365 x 10 -6} where AR 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

16. Identification of High Crash Locations 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 AR = N / {[Sum (ADT)s /2] x 365 x 10 -6} AR = 25/ {26,500/2] x 3 yrs x365 x 10 -6} AR = 1.72 crashes per million entering vehicles

17. Identification of High Crash Locations Collision Types at Rural Intersections

18. Identification of High Crash Locations 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.

19. Identification of High Crash Locations Step 2: Characterize the Crash Experience Prepare a Collision Diagram

20. Step 3: Characterize Field Conditions Identification of High Crash Locations

21. Step 3: Characterize Field Conditions Traffic Data Studies: Identification of High Crash Locations  Traffic Volume – Turning Movement, ADT  Spot Speeds  Traffic Conflict Study  Sight Distance Evaluation

22. Non-Crash Based Procedures Identification of High Crash Locations

23. Step 4: Identify Contributing Factors and Appropriate Countermeasures Identification of High Crash Locations *Table 12, from Missouri HAL Manual

24. Step 5: Assess Countermeasures and Select Most Appropriate Identification of High Crash Locations

25. Probable Causes for Crash Patterns and Engineering Countermeasures Identification of High Crash Locations Rear-End Collisions at un-signalized intersection

26. Identification of High Crash Locations Documents list “Crash Reduction Factors” (CRF) and “Accident Modification Factors” (AMF) for specific types of crashes –CRF : (+) number is % reduction in crash type (-) number is % increase in crash type

27. Identification of High Crash Locations “Accident Modification Factors” (AMF) for specific types of crashes –AMF : ratio of (after) crashes / (before) crashes AMF < 1 means a reduction in crash type AMF > 1 means an increase in crash type – AMF = 1- CRF

28. Estimated Crash Reduction Factors Identification of High Crash Locations Install Warning Signs

29. Estimated Crash Reduction Factors Identification of High Crash Locations * From MN DOT Traffic Safety Fundamentals Handbook

30. Traffic Crash Costs: Identification of High Crash Locations *NCHRP 440

31. Traffic Crash Costs: Identification of High Crash Locations * From MN DOT Traffic Safety Fundamentals Handbook

32. Typical Benefit/Cost Ratios Identification of High Crash Locations * From MN DOT Traffic Safety Fundamentals Handbook

33. Step 6: Implement Countermeasures and Evaluate Effectiveness Identification of High Crash Locations Improve Sight Distance – 5% Crash Reduction per Quadrant – 20% for all 4 quadrants

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

35. Questions? Identification of High Crash Locations