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

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

Provide advance guide signs and street name signs

Photo Source: NCHRP Report 500 Series Volume 9

Background

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

Provide advance guide signs and street name signs

Photo Source: NCHRP Report 500 Series Volume 9

Background

Differing methods to provide street names in advance of intersection:

Photo source: NCHRP Report 500 Series Volume 9 and North Carolina Dept of Transportation (http://www.ncdot.org/doh/preconstruct/traffic/ECHS/groups/docs/int/Advance.pdf)

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

Status of Data Collection

Crash data from 1997-2004 400 intersection-years of

before crash data  300 intersection-years of

after crash data 

North Carolina Blanketed strategy in Cary, NC in 2001 100 sites included in the study

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

Study Design

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

Questions?