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Low Cost Safety Improvements Pooled Fund Study

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.

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Low Cost Safety Improvements Pooled Fund Study

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  1. Low Cost Safety Improvements Pooled Fund Study Advanced Street Name Signs Dr. James Jenness, Westat

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

  3. 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 Photo Source: NCHRP Report 500 Series Volume 9

  4. Background Provide advance guide signs and street name signs • 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 Photo Source: NCHRP Report 500 Series Volume 9

  5. Background • 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 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)

  6. Data Collection

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

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

  13. Questions?

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