Low Cost Safety Improvements
Pooled Funds Study

Safety Evaluation of STOP AHEAD Pavement Markings

Overview

• Introduction
• Objective
• Study Design
• Data Collection
• Results
• Economic Analysis
• Conclusions

Background on Strategy

STOP AHEAD Tried Low cost Short-term implementation Target crashes Right-angle Rear-end Other STOP sign violation crashes Potential Difficulties Visibility in winter Low coefficient of friction Key to Success Maintenance of markings

Literature Review

• STOP AHEAD pavement markings
  • No available literature
• STOP AHEAD signs
  • Several studies
  • Not particularly effective (Zwahlen, 1988)

Objective

• Estimate Safety Effectiveness
  • Total crash frequency
  • Target crash frequency
    • Right-angle collisions
    • Rear-end collisions
    • Injury collisions
• Questions of Interest
  • Do effects vary by:
    • Traffic volumes?
    • Area type?
    • Number of approach legs?
    • Number of stop-controlled approaches?
  • Is the treatment economically feasible?

Study Design

• Required Sample Size
  • Minimum: 53 intersection-years
    • Detect 20 percent reduction in total crashes with 90 percent confidence
  • Desirable: 260 intersection-years
    • Detect 10 percent reduction in total crashes with 90 percent confidence
• Assumptions
  • Number of reference sites = number of strategy sites

Data Collection

Data Collection – Arkansas

Total number of intersections used = 8

Data Collection – Maryland

Total number of intersections used = 9

Data Collection – Minnesota

Total number of intersections used = 158

Evaluation Results

Aggregate Analysis

Note: A negative sign indicates an increase in crashes.
Bold numbers indicate a statistically significant effect (95% confidence level).

Note: A negative sign indicates an increase in crashes.
Bold numbers indicate a statistically significant effect (95 percent confidence level).

Disaggregate Analysis

Note: A negative sign indicates an increase in crashes.
Bold numbers indicate a statistically significant effect (95% confidence level).

Economic Analysis

Determine the Annual Cost of Installation

• States Provided Installation Costs and Service Life
  • Latex: $140 per approach (2 year service life)
  • Thermoplastic: $1,500 per approach (5 year service life)
• Convert Installation Cost to Annual Cost
  • Latex: $78 per approach/year
  • Thermoplastic: $366 per approach/year

Estimate Crash Costs

• FHWA Unit Crash Cost Data (Council et al., 2005)
  • $58,832 for undefined collision
  • Includes "hard dollar" and "non-monetary" costs
• Assume 2:1 Benefit-Cost Ratio
• Required Crash Reduction (2:1 Benefit-Cost Ratio)
  • Latex: 0.005 (Two-way stop- controlled) or 0.011 (All-way stop- controlled)
  • Thermoplastic: 0.025 (Two-way stop- controlled) or 0.050 (All-way stop- controlled)

Conclusions

• Total Crashes
  • Significant reduction in AR, MD, and overall
• Right-angle and Rear-end Crashes
  • Significant reduction in AR
• Injury Crashes
  • Significant at 10 percent level overall
• Disaggregate Analysis
  • Greater effect for 3-legged (highly significant)
  • Greater effect for All-way stop-controlled (highly significant)
  • Some variation by AADT

• General Reduction in Crashes
  • Results supported by MN data
    
• Economically Feasible
  • Low cost strategy
  • Modest reduction to achieve 2:1 Benefit-Cost ratio
  • Necessary reduction is easily achievable

Benefit >> Cost

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