Diagnosis of Sites with Potential for Safety Improvement

1. Module 4 Diagnosis of Sites with Potential for Safety Improvement Safety Analysis in a Data-limited, Local Agency Environment July 22, 2013 - Boise, Idaho

2. Module 4 Objectives • Develop and use diagnostics • Describe different approaches to safety and how diagnostics differ across these approaches • List studies that can support diagnostics • Site visits • Collision diagrams • Assessment of human factors • Road safety audits/ assessments

3. Diagnostic Questions What are the characteristics of the areas of interest identified in Module 3? • Geometry, roadside, safety features, operational characteristics What are the characteristics of the people involved in the crashes? • User age, purpose of trips, mode choice, safe/unsafe behaviors What are the characteristics of the crashes themselves? • Over-represented crash types and characteristics

4. Site-specific & systemic approaches

5. Site-specific & systemic approaches Most agencies use a combination of these approaches • to treat locations with the highest potential for improvement • to reduce risk of possible events by implementing low cost treatments system wide (systemic) Often, a combination of strategies can have the greatest return on investment in safety (benefit-cost ratio)

6. Site-specific Diagnosis We can gather information for diagnosis through one or more of these methods: • Site visit • Crash history • Local knowledge • Crash Analysis Safety Study (would include site visits and incorporating local knowledge) • Road safety audit/road safety assessments

7. Road Safety Studies A road safety study may require several elements or activities (the nature of the site governs what is needed): • Crash history analysis • Site observations: user behavior, specific traffic control features, changes in traffic flow and characteristics over different times of the day • Operating speed study • Other • Traffic volume counts • Access management study • Origin-destination study

8. Site Visits

9. Creating Collision Diagrams Building a collision diagram from crash reports • Reflect actual roadway geometry and features and scale to the extent possible • Symbols used for various crash types • Denoting severity level, vehicle type, other variables • Labeling: what information are you interested in or would be most relevant for your site?

10. Creating Collision Diagrams

11. Creating Collision DiagramsSymbols & summary tables

12. Creating Collision Diagrams Individual collisions can be listed on a collision summary This can be done by hand on a paper form, in readily available presentation software, or by using diagraming software The most important: the diagram should help us distinguish patterns or specific characteristics of crashes at the site

13. Creating Collision DiagramsExample of summary for collision diagram

15. Interpreting Collision Diagrams The value of collision diagrams: identifying • Relative frequency of crash types (crash manner) • Which approaches/ movements have the highest crash involvement • Days of week or times of day that are overrepresented • Geometric design issues that may be also contributing

16. What can we learn from the diagram? Is any information missing?

18. Users and contextUnderstanding the Users Who are involved in crashes at this location? Consider the following: • Vulnerable users (peds, bikes, motorcycles, users with disabilities) • Driver ages (young, mature) • Trip types (commuters, recreational trips, school trips) • Different modes, including transit and freight vehicles Why are they behaving the way they are? What are their needs?

19. Human Factors2nd Edition of the Human Factors Guidelines NCHRP Report 600 • What are the errors that drivers and users are making? • Is driver expectation violated? • What are we expecting the driver to do? • Judging distance and speed • Inattentional blindness • Visibility • Etc.

20. Local Knowledge The local community uses the facility the most – and can offer valuable insights Examples: • Law enforcement: • crash locations where people are killed or seriously injured • Locations and particular crash types (DUI, speeding, etc.) • Local maintenance staff know objects being continually hit and replaced or how often sight-distance blocking foliage is trimmed, etc.

21. Road Safety Audits Independent, multi-disciplined group: engineers, law enforcement, planners, elected officials, user group advocates, educators, etc. Planned or existing facilities (most beneficial for planning or early in the design process) Includes site visit Consider multiple modes and their interactions Consider human factors Both diagnose (this module) and recommend countermeasures (next module) Result in a report of findings and recommendations presented to facility owner

22. Making the connection Diagnosis is our tool to identify • Which of the fatal and serious injury crashes are the most common? • What are the most common contributing factors? • Who are the users we need to consider? Diagnosis is the key to identifying the most appropriate countermeasure/ combination of countermeasures for target crash types and considering the context in the process (the role of the facility, land use, etc.)

23. Summary • Two ways to approach diagnosis: at individual sites, or at similar sites across the system • Several means of gathering data for diagnosis • Crash history and diagrams • Site visits • Road safety study to gather volume, traffic patterns, speeds, etc. • RSAs and local knowledge • Aim to identify contributing factors to crashes before you can choose appropriate countermeasures

24. End Module 4 Questions?