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Low Cost Safety Improvements Pooled Fund Study
Advanced Street Name Signs
Dr. James Jenness, Westat
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Overview
Background Status of Data Collection Study Design Remaining Data Needs Evaluation Considerations
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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
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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
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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
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Data Collection
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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
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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
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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
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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
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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
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Evaluation Considerations
Do not have large enough sample size
Comparing two methods of signing
Limited ADT data in Massachusetts
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Questions?