Lecture 22: Traffic Conflicts Technique

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Highway Traffic and Safety Analyses
Lecture 22 Traffic Conflicts Technique
Purdue University School of Civil
Engineering West Lafayette
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Outline

• Concept
• On-site observations
• Analyses

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Concept Traffic Conflict

• Traffic conflict occurs when one or two drivers
  have to rapidly slow down or swerve to avoid
  collision with another vehicle.

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Concept Time to Collision

• Time to collision (TTC) is the time measured
  between the moment of the evasive action
  beginning and the hypothetical moment of
  collision if the evasive action was not taken.

Distance
Hypothetical trajectory of the vehicle
Time
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Concept Time to Collision
TTC Score TTC (s) Risk of collision
1 1.5-2.0 Low
2 1.0-1.5 Moderate
3 0.0-1.0 High
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Concept Time to Collision

• Time-to-collision zones correspond to the TTC
  ranges
• 0.0-1.0,
• 1.0-1.5,
• 1.5-2.0.

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Concept Secondary Conflict
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Concept Secondary Conflict
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Concept Secondary Conflict
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Concept Traffic Conflict Types
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Concept Traffic Conflict Types
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On-site Observations - Field Form
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On-site Observation - Observers
TWSC intersection requires 2 for 16 hours (two
days)
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On-site Observation - Observers
Signalized intersection requires 4 observers for
8 hours or 2 observers for 16 hours
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On-site Observations - Training

• Day One Fundamentals of Traffic Conflicts
  Technique
• Day Two First and Second Field Observations and
  Debriefing
• Day Three Third and Fourth Field Observations
  and Debriefing
• Compressed program does not include the third day

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Analysis

• Distribution by type
• Spatial distribution
• Conflict frequency
• Conflict severity
• Temporal distribution
• Conflict causes and interpretation

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Analysis
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Analysis Spatial Distribution
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Analysis - Average Hourly Conflicts
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Analysis - Average Hourly Conflicts per Thousand
Entering Vehicles
AHC/TEV AHC1,000/Average Hourly Volume
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Summary of Conflict Characteristics
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Reading Assignment

• http//www.tft.lth.se/rapporter/Conflict1.pdf

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References
G.D. Hamilton Associates Consulting Ltd., Traffic
Conflict Procedures, Manual, Second Edition,
Insurance Corporation of British Columbia,
November 1996