Low Cost Safety Improvements Pooled Fund Study

Advanced Street Name Signs

Dr. James Jenness, Westat

Overview

• Background
• Status of Data Collection
• Study Design
• Remaining Data Needs
• Evaluation Considerations

Background

Provide advance guide signs and street name signs

Ranked 14th NCHRP Report 500 Series Older Driver Guidebook Older drivers are more involved in intersection crashes than other drivers Older drivers exhibit excessive vehicle-braking at/before intersections
Tried, low cost, short-term implementation Target crashes All intersection related Rear-end Late lane changes Night Older drivers Consistent signing across jurisdictions also important

• Differing methods to provide street names in advance of intersection:

  Green and white Advance Street Name signs
  	MUTCD W3-3 advance traffic control signs with W16-8 supplemental warning plaques

Data Collection

Status of Data Collection

Massachusetts Blanketed strategy across four districts in 2004 200 sites included in the study Over 400 installed Lack of ADT data limited sample Limited crash data 2002-2005 500 intersection-years of before crash data 250 intersection-years of after crash data

North Carolina Blanketed strategy in Cary, NC in 2001 100 sites included in the study Crash data from 1997-2004 400 intersection-years of before crash data 300 intersection-years of after crash data

Study Design

• Required Sample Size
  • Minimum: 803 intersection-years per period
    • Detect a 5 percent reduction in total crashes with 95 percent confidence
  • Desirable: 2,031 intersection-years per period
    • Detect a 10 percent reduction in older driver crashes with 95 percent confidence
• Assumptions
  • 7.0 crashes per intersection per year in the before period, of which 9 percent involve older drivers
    • Crash rate based on preliminary data from MA sites, older-driver share based on Toronto data
  • Before and after periods are of equal length
  • Equal number of intersection-years for treatment and reference sites

Remaining Data Needs

• Minimum: Need 450 more after intersection-years
• Desirable: Need 1,130 before intersection- years and 1680 after intersection-years for older driver
• Need additional installations

Evaluation Considerations

• Do not have large enough sample size
• Comparing two methods of signing
• Limited ADT data in Massachusetts

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