Session #5 Crash Diagnosis & Selecting Countermeasures

1. HSM Roadway Safety Management Process Session #5 Crash Diagnosis & Selecting Countermeasures

2. Crash Diagnosis and Selecting Countermeasures • Describe the activities involved with Crash Diagnosis Process • Crash Patterns • Past Studies • Physical Characteristics • Selecting Countermeasures to Reduce Crash Frequency • Identify Contributing Factors • Identify Countermeasures That Addresses the Contributing factors Learning Outcomes:

3. Crash Diagnosis and Selecting Countermeasures Diagnosis Chapter 5 • Diagnosis = evaluation to identify crash patterns using: • Past studies to identify known issues • Physical characteristics of the site • Driver behavior at the site • Other Information

4. STEP 1: Review safety data STEP 2: Assess supporting documentation Personal testimony STEP 3: Assess field conditions Desired Outcomes Understand site conditions Identify crash patterns Gain insight on countermeasure selection Diagnosis Process Crash Diagnosis and Selecting Countermeasures

5. Crash Diagnosis and Selecting Countermeasures Safety Data Review • Descriptive Crash Statistics • Crash conditions (date, day of week, time of day) • Crash type (rear-end, angle, sideswipe, etc) • Crash severity (KABCO) • Environmental conditions • Sequence of events • Direction of Travel • Contributing factors • Weather, Lighting Conditions, Road Conditions, Impaired Drivers/Pedestrian • Individual Crash Reports

6. Intersection A Collision Diagram (example) Crash Diagnosis and Selecting Countermeasures

7. Crash Diagnosis and Selecting Countermeasures Diagnosis Tools: Condition Diagram for Intersection (example) • Visual site overview • Can be overlaid on collision diagram

8. Crash Diagnosis and Selecting Countermeasures Conduct Actual Site Visit: • Roadway Characteristics • Traffic Conditions • Driver Behavior • Land Uses • Verified Field Review of Intersection A • Signalized intersection • Left turn lanes in all quadrants • Permissive/protected phasing • Pedestrian crossings and signal control • Clearance interval not adequate for prevailing speeds

9. Identified Crash Types at Intersection A (example) Crash Diagnosis and Selecting Countermeasures

10. Crash Diagnosis and Selecting Countermeasures Diagnosis Tools Other Support Documentation • Land use maps • Historic weather patterns • Public comment records • Roadway improvement plans • Anecdotal information

11. Crash Diagnosis and Selecting Countermeasures Summary - Safety Diagnosis Essentials • Data of sufficient quantity and quality • Field observations • Diagnostic tools • Knowledge • Safety fundamentals • Human factors • Traffic and highway engineering • Good judgment

12. Crash Diagnosis and Selecting Countermeasures Select Countermeasures Chapter 6 • Identify contributing crash factors • Identify and select countermeasures

13. Crash Diagnosis and Selecting Countermeasures Select Countermeasures(CHAPTER 6) • Identify contributing factors • Select potential countermeasures or treatments • Apply countermeasures

14. Crash Diagnosis and Selecting Countermeasures Identify Contributing Factors

15. HSM Part B – Selecting Countermeasures Five HSM Categories for Crash Contributing Factors: • Crashes on Roadway Segments • Crashes at Signalized Intersections • Crashes at Unsignalized Intersections • Crashes at Highway-Rail Grade Crossings • Crashes involving Pedestrians & Bicyclists

16. HSM Part B - Selecting Countermeasures Contributing Factors: A. Crash Types on Roadway Segments • Vehicle Rollover • Fixed Object • Nighttime • Wet Pavement • Opposite-Direction • Run-Off-Road • Bridges

17. HSM Part B - Selecting Countermeasures Contributing Factors: B. Crash Types at Signalized Intersections • Right-Angle • Rear-end or Sideswipe • Left or Right Turn • Nighttime • Wet Pavement

18. HSM Part B - Selecting Countermeasures Contributing Factors: (C) Crash Types at Unsignalized Intersections • Right-Angle • Rear-end • Collisions at Driveways • Head-on or Sideswipes • Left or Right Turn • Nighttime • Wet Pavement

19. HSM Part B – Selecting Countermeasures Contributing Factors: (D) Crashes at Highway-Rail Grade Crossings

20. HSM Part B – Selecting Countermeasures Contributing Factors: (E) – 1. Crashes involving Pedestrians

21. HSM Part B – Selecting Countermeasures Contributing Factors: (E) - 2. Crashes involving Bicyclists

22. Crash Diagnosis and Selecting Countermeasures Select Potential Countermeasures • Three Main Steps: • Identify factors contributing to crashes at the site • Identify countermeasures that address the contributing factors • Conduct cost-benefit analysis to select preferred treatments

23. Selecting Potential Countermeasures - Example Crash Diagnosis and Selecting Countermeasures

24. Step 1 (a) – Indentify Target Crash Types Crash Diagnosis and Selecting Countermeasures • What factors are likely contributing to the target crash types?

25. Crash Diagnosis and Selecting Countermeasures Step 1 (b) – Indentify Contributing Factors • Contributing Factors for Angle Crashes: • Restricted sight distance • High traffic volume • High approach speeds • Unexpected crossing traffic • Driver running stop sign • Slippery pavement • Contributing Factors for Head-On Crashes: • Inadequate pavement markings • Narrow lanes

26. Crash Diagnosis and Selecting Countermeasures Step 2 – Indentify Countermeasures to address the Contributing Factors CountermeasureCrash TypeCMFTable # Convert to modern Roundabout All 0.61 14-4 Convert to All-Way Stop Angle 0.25 14-5 Convert to Signalized Control All 0.95 14-7 Angle 0.33 14-7 Install Lt-Turn Lanes 2 Approaches All 0.53 14-12 Injury 0.50 14-12 Install Lighting if not present Nighttime Inj 0.62 14-18 Install Flashing Beacons Angle 1.12 14-22 (Urban Stop-Control)

27. Crash Diagnosis and Selecting Countermeasures Step 3 – Conduct cost-benefit analysis to select preferred treatments (Chapter 7) • Determine benefits from implementing countermeasure(s): • Expected change in average crash frequency or severity converted to monetary values • Benefits can include reduce travel time, congestion relief, and lesser environmental impacts • Compared to cost of implementing the countermeasure

28. Crash Diagnosis and Selecting Countermeasures • Described the activities involved with Crash Diagnosis Process • Crash Patterns • Past Studies • Physical Characteristics • Selecting Countermeasures to Reduce Crash Frequency • Identify Contributing Factors • Identify Countermeasures That Addresses the Contributing factors Learning Outcomes:

29. Crash Diagnosis and Selecting Countermeasures Questions and Discussion