1. NC Local Safety Partnership Selecting Interventions

2. Workshop Roadmap Program Background and Overview Understanding Crash Data Identifying Potential Treatment Locations Preparing Collision Diagrams Selecting Interventions Evaluation Methods Program Implementation and Discussion 2

3. Module Objectives ￭ Use safety data and site investigation to explore problem areas ￭ Identify contributing crash factors and select appropriate countermeasures ￭ Conduct benefit-cost analysis to guide countermeasure implementation 3

4. Steps for Selecting Interventions Review safety dataInvestigate site Identify potential contributing factors Identify and list potential countermeasures Conduct benefit-cost analysis 4

5. STEP 1 – REVIEW SAFETY DATA Module 5 – Selecting Interventions 5

6. Safety Data Review ￭ Descriptive statistics ￭ Crash type ￭ Crash severity (KABCO) ￭ Environmental conditions ￭ Event sequence ￭ Crash locations ￭ Supporting documentation 6

7. Descriptive Statistics: Crash Type 7

8. Descriptive Statistics: Crash Severity 8

9. Descriptive Statistics: Environmental Conditions 9

10. Event Sequence 10

11. Crash Locations: Collision Diagram 11

12. Supporting Documentation ￭ Land use maps ￭ Historic weather patterns ￭ Public comment records ￭ Roadway improvement plans ￭ Anecdotal information 12

13. STEP 2 – INVESTIGATE SITE Module 5 – Selecting Interventions 13

14. Site Investigation ￭ Investigate site to observe field conditions ￭ Verify if site characteristics agree with details on crash report ￭ Drive both directions of a road segment or each approach of an intersection ￭ Observe traffic movements and signal timing at various points during the day ￭ Evaluate sight distance 14

15. Site Investigation ￭ Note locations of driveways and other access points ￭ Observe use by non-motorized users (i.e., where are pedestrians crossing?) ￭ Take photos ￭ Look for evidence of safety issues (tire marks on curb, pole damage, broken glass on pavement, etc.) ￭ Construct condition diagram for later reference 15

16. Condition Diagram Light Pole Pothole Driveway Tree Sidewalk School Playground Bank 16

17. Example of Verified Field Review ￭ Signalized intersection ￭ Left turn lanes in all quadrants ￭ Permissive/protected phasing ￭ Pedestrian crossings and signal control ￭ Clearance interval not adequate for prevailing speeds 17

18. STEP 3 – IDENTIFY CONTRIBUTING FACTORS Module 5 – Selecting Interventions 18

19. Identify Contributing Factors Roadway HumanVehicle 19

20. ￭ Potential contributing factors are provided in the AASHTO Highway Safety Manual for: ￭ Roadway Segments ￭ Signalized Intersections ￭ Unsignalized Intersections ￭ Highway-Rail Grade Crossings ￭ Pedestrians ￭ Bicyclists Contributing Crash Factors 20

21. Example Possible Contributing Factors Signalized Intersections (See p. 6-5 and 6-6 of the HSM ) 21

22. Contributing Factors for Severe Crash Types Angle and turning (left) ￭ Misjudging speed of opposing traffic ￭ Visibility of signals ￭ Inadequate signal timing Rear end (east approach) ￭ Inappropriate or excessive approach speeds ￭ Unexpected stops (driveways/access) 22

23. Example ￭ Two-way stop-controlled intersection ￭ Four legs ￭ Major road AADT = 22,100 ￭ Minor road AADT = 1,650 ￭ Urban area 23

24. Example 3-Year Crash Total Predominant Crash Types Crash Severity FatalInjuryPDO 35Angle, Head- on 6%65%29% What are the likely contributing crash factors? 24

25. STEP 4 – IDENTIFY AND LIST POTENTIAL COUNTERMEASURES Module 5 – Selecting Interventions 25

26. Sources for Potential Countermeasures ￭ Roadway Countermeasures ￭ NCHRP Series 500 ￭ Highway Safety Manual, Part D ￭ FHWA Crash Modification Factor Clearinghouse ￭ FHWA list of suggested (proven) countermeasures ￭ Behavioral Countermeasures ￭ Countermeasures That Work 26

27. Countermeasure Sources: NCHRP Series 500 Guides Countermeasures classified as: 1.Proven, 2.Tried, or 3.Experimental Examples: Relocate roadside objects (P) Install shoulder rumble strips (T) Delineate poles with retroreflective tape (E) 27

28. Countermeasure Sources: Highway Safety Manual ￭ First edition released in 2010 ￭ Provides practitioners with the best factual information and tools regarding safety consequences of design decisions. ￭ Sections ￭ Part A: Safety knowledge ￭ Part B: Safety management ￭ Part C: Crash prediction models ￭ Part D: Countermeasure selection and CMFs 28

29. Countermeasure Sources: Crash Modification Factors Clearinghouse 29

30. Countermeasure Sources: FHWA Suggested Countermeasures (2008) ￭ Road safety audits ￭ Roundabouts ￭ Left and right turn lanes at stop-controlled intersections ￭ Yellow and all red change intervals at traffic signals ￭ Median and pedestrian refuge areas in urban and suburban areas ￭ Walkways 30

31. Countermeasure Sources: NHTSA “Countermeasures That Work” 31

32. Question ￭ When faced with many potential countermeasures, how do you choose which one(s) to implement? 32

33. Comparing Countermeasures ￭ Subjective comparisons are important… ￭ Which will garner the most public support? ￭ Which is most appropriate for the area? ￭ …But objective comparisons are priority ￭ Expected effectiveness -> decreases in crashes (CMFs) ￭ Expected costs -> installation and maintenance 33

34. STEP 5 – CONDUCT BENEFIT- COST ANALYSIS Module 5 – Selecting Interventions 34

35. Countermeasure Costs ￭ Startup or installation costs ￭ Example? ￭ Ongoing operational or maintenance costs ￭ Example? ￭ Resilience/staying power (“usable life”) ￭ Which countermeasures would have shorter staying power? Which would be longer? 35

36. Countermeasure Benefits ￭ Crashes prevented – use CMFs to estimate if available ￭ Changes in crash severity ￭ Ex: Signals and red light cameras ￭ Ex: Cable median barriers ￭ Other benefits not related to safety (e.g., reduced delay) 36

37. Countermeasure Benefits: Crash Modification Factors ￭ Crash modification factor (CMF) is a multiplicative factor used to compute the expected number of crashes after implementing a given countermeasure at a specific site. ￭ CMF = ￭ CMF > 1 indicates an expected increase in crashes ￭ CMF < 1 indicates an expected decrease in crashes Expected crashes with countermeasure Expected crashes without countermeasure 37

38. Countermeasure Benefits: Crash Modification Factors 38

39. Countermeasure Benefits: Assigning Monetary Value to Crashes Prevented ￭ Complex Process ￭ Rules of Thumb ￭ Fatal plus Serious Injury vs. minor injury plus PDO Costs ￭ Cost Effectiveness 39

40. Countermeasure Benefits: NCDOT Crash Cost Resource 40

41. Countermeasure Benefits: NCDOT Crash Costs 2011 41

42. Benefit-Cost Analysis ￭ Striving for the most effective use of limited safety funds (“bang for the buck”) ￭ Rank competing projects ￭ Methods ￭ Benefit-cost ratio ￭ Present value of benefits 42

43. Example: Benefit-Cost Ratio ￭ Proposed: Install left turn lane at signalized intersection ￭ Cost: ￭ $168,000 for construction and $32,000 for right-of-way ￭ Annual cost over 22-year service life is $19,700 ￭ Benefit: ￭ Expected to reduce 6 crashes per year ￭ Equivalent to $187,300 in annual crash cost savings 43

44. Example: Benefit-Cost Ratio ￭ Annual cost = $19,700 ￭ Annual benefit = $187,300 ￭ Benefit-cost ratio 44 187,300 19,700 = 9.5

45. Other (Qualitative) Considerations ￭ What are other considerations that can play a role in which countermeasures are implemented? 45

46. Other (Qualitative) Considerations ￭ Design Standards ￭ Tradeoffs ￭ Familiarity ￭ Constituent Concerns 46

47. Take Away Messages ￭ Reviewing safety data (and supporting documentation) is a critical first step ￭ Field reviews reveal problems that may not be apparent in data review ￭ By identifying other contributing factors, countermeasures can be selected to best address crash problem ￭ Benefit-cost analysis can help prioritize and guide improvements 47