low cost safety improvements pooled fund study
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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. - PowerPoint PPT PresentationTRANSCRIPT
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?