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

Overview u Background u Status of Data Collection u Study Design u Remaining Data Needs u Evaluation Considerations

Background u Ranked 14 th u NCHRP Report 500 Series Older Driver Guidebook u Older drivers are more involved in intersection crashes than other drivers u 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 u Tried, low cost, short-term implementation u Target crashes l All intersection related l Rear-end l Late lane changes l Night l Older drivers u Consistent signing across jurisdictions also important Provide advance guide signs and street name signs Photo Source: NCHRP Report 500 Series Volume 9

Background u Differing methods to provide street names in advance of intersection: Photo source: NCHRP Report 500 Series Volume 9 and North Carolina Dept of Transportation ( l Green and white Advance Street Name signs l MUTCD W3-3 advance traffic control signs with W16-8 supplemental warning plaques

Data Collection

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

Status of Data Collection l Crash data from l 400 intersection-years of before crash data l 300 intersection-years of after crash data u North Carolina l Blanketed strategy in Cary, NC in 2001 l 100 sites included in the study

Study Design u Required Sample Size l Minimum: 803 intersection-years per period Detect a 5 percent reduction in total crashes with 95 percent confidence l Desirable: 2,031 intersection-years per period Detect a 10 percent reduction in older driver crashes with 95 percent confidence

Study Design u Assumptions l 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 l Before and after periods are of equal length l Equal number of intersection-years for treatment and reference sites

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

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

Questions?