Chapter 2: Solving Traffic Safety Problems

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Chapter 2 Solving Traffic Safety Problems

• Overview
• Problem Solving
• Information Gathering
• Identifying Contributory Factors
• Selecting the Appropriate Countermeasure
• Evaluating Success
• Prioritizing Improvements

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Problem Solving Technique

• 1. Identify problem
• 2. Select appropriate countermeasure
• 3. Install countermeasure
• 4. Evaluate countermeasure effectiveness
• 5. If not effective, return to Step 1

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Information Gathering

• Identify the problem?
• Define whats causing it?
• Information sources

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What is the Problem?

• Describe symptoms
• Right-angle crashes at intersection
• Crashes happen on rainy days
• Look for commonalities
• They often point to the cause

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Information Sources

• Public
• Police
• Emergency medical service
• Crash records
• Go out and look (site inspection)

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Condition Diagrams
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Collision Diagrams

• Identify common crash types or conditions
• Need police crash reports to construct
• May require several years of crash records

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Crash Mapping
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A More Detailed Look
12/31/01,night,snow,dui
2/5/12, day, wet
9/25/99, day, dry
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Road Safety Audits

• Formal safety examination by independent review
  team
• Proactive approach to look for potential safety
  problems
• Can take place at any stage of project
• Audit teams rank urgency of safety defects
• Always document safety issues and develop a plan
  to address them

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Whats Causing It?

• Does a road condition contribute?
• Traffic control?
• Road conditions?
• Could a change to the road help?
• Prevent driver error?
• Provide room to recover?
• Reduce severity?

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Selecting Countermeasures

• What kind of crashes are you trying to prevent?
• For example, rear-end or wet weather
• Choose the one that best fits problem
• Watch for unintended consequences

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Install Appropriate Countermeasure
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Is It Working?

• Before and after study
• Observe traffic
• May need to try again

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Evaluate Effectiveness Example
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Prioritize Work

• Do what you can,
• where you are,
• with what you have.
• T. Roosevelt

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Priority Levels

1. Urgent - immediate attention needed
2. High - improve in the near future
3. Medium - improve as priority allows
4. Low - improve when other work is done to road

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Priority
SEVERITY FREQUENCY FREQUENCY FREQUENCY
SEVERITY Frequent Occasional Rare
Fatal URGENT HIGH MEDIUM
Serious HIGH MEDIUM LOW
Minor MEDIUM LOW LOW
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Other Priority Factors

• Which intersection comes first?
• Why?
• Which one is easier to fix?
• Which is cheaper?

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Balancing Safety, Environment, Cost
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Think Long Term
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Think Long Term
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Documentation

• Defense against litigation
• Highway defect complaints
• Patrols and condition surveys
• Sign inventories
• Traffic studies

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What to Document

• What, Where, When, Who, Why, How
• Document even if no defects found

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Summary

• Problem solving procedure
• Prioritizing safety improvements
• Documentation