low cost safety improvements pooled funds study increasing retroreflectivity of stop signs results
DESCRIPTION
Low Cost Safety Improvements Pooled Funds Study Increasing Retroreflectivity of STOP Signs Results. Dr. Bhagwant Persaud, Persaud and Lyon, Inc. Overview. Introduction Objective Study Design Data Collection Results Economic Analysis Conclusions. Background on Strategy. - PowerPoint PPT PresentationTRANSCRIPT
Low Cost Safety Improvements Pooled Funds Study
Increasing Retroreflectivity of STOP Signs Results
Dr. Bhagwant Persaud, Persaud and Lyon, Inc
Overview
Introduction Objective Study Design Data Collection Results Economic Analysis Conclusions
Background on Strategy
Identified by TAC, not in Guides Low-cost, short-term
implementation Target crashes
Right-angle Other STOP sign violation
Literature Review
Legibility effects of increasing the retroreflectivity of freeway guide signs (Carlson and Hawkins)
No studies on increased retroreflectivity levels of STOP signs
Objective
To estimate the safety effectiveness of increasing the retroreflectivity of STOP signs as measured by crash frequency
To assess cost-effectiveness Questions of interest
Do effects vary by traffic volumes? Do effects vary by land use (i.e., urban/rural) Do effects vary by type of interest (i.e., 3 versus 4-leg)
Study Design
Sample Size Minimum 1,076 intersection years per period to detect
a 20percent reduction in right angle crashes Desirable 2,036 intersection years per period to detect a
10percent reduction in all crashes Assumes 0.44 crashes per intersection per year before
strategy of which 0.17 are right angle crashes
Data Collection
Data Collection
Variable Connecticut (231)
South Carolina
(108)Months Before 59.7 100.7
Months After 46.2 42.1
Crashes/site-year before 1.9 2.1
Crashes/site-year after 2.4 2.0
Injury crashes/site-year before 0.7 0.7
Injury crashes/site-year after 0.8 0.6
Right-angle crashes/site-year before 0.5 0.8
Right-angle crashes/site-year after 0.6 0.7
Rear-end crashes/site-year before 0.9 0.7
Rear-end crashes/site-year after 1.4 0.7
Data Collection
Variable Connecticut (231)
South Carolina
(108)Daytime crashes/sites-year before 1.4 1.7
Daytime crashes/site-year after 1.8 1.6
Nighttime crashes/site-year before 0.5 0.4
Nighttime crashes/site-year after 0.6 0.4
Major road AADT before 7,690 9,847
Minor road AADT before 2,033 2,017
Major road AADT after 8,021 10,414
Minor road AADT after 2,122 2,139
Aggregate Evaluation Results
States
Percent reduction in Right Angle
Crashes
Percent reduction in Rear-
end Crashes
Percent reduction in Night Crashes
Percent reduction
in Day Crashes
Percent reduction in Injury Crashes
Percent reduction in Total Crashes
CT -5.8 -9.7 6.6 -3.2 6.0 -0.2
SC 7.6 17.5 -4.4 9.1 9.4 5.4
ALL -1.2 -2.2 4.4 -0.1 6.7 1.2
Aggregate Evaluation Results(Continued)
State
Percent reduction in crashes (standard error)
Standard Error of
Right Angle
Crashes
Standard Error of Rear-end Crashes
Standard Error of
Night Crashes
Standard Error of
Day Crashes
Standard Error of Injury
Crashes
Standard Error of
Total Crashes
CT 6.2 5.7 5.5 3.6 4.8 3.1
SC 7.6 7.3 10.8 5.3 8.1 4.9
ALL 5.3 4.8 6.0 2.7 4.5 2.7
Disaggregate Group SitesPercent reduction
of all crashes
SC urban 47 13.7SC rural 61 -2.0CT urban 190 -2.2CT rural 41 15.4
Disaggregate Evaluation Results: Urban versus Rural
Disaggregate Group Sites Percent reduction
CT 3-legged 172 4.1CT 4-legged 59 -11.6CT 3-legged, rural 29 23.1CT 4-legged, rural 12 -0.2SC 3-legged 48 15.9SC 4-legged 60 -5.3SC 3-legged, urban 20 26.3SC 4-legged, urban 27 0.05
Disaggregate Evaluation Results 3-leg versus 4-leg
Disaggregate Group Sites Percent reduction
SC < 1200 minor AADT 42 24.9SC > 1200 minor AADT 66 -3.4CT < 1000 minor AADT 90 14.3CT >1000 minor AADT 141 -5.1
Disaggregate Evaluation: Effect of Minor ADT
Economic Analysis
FHWA cost per crash for unsignalized intersections $13,238 for rear-end $61,114 for right angle
$66/year crash savings per intersection required for a 2:1 benefit cost ratio
Requires 0.005 rear-end crashes saved per intersection per year
Target seems easily achievable – especially under favorable circumstances identified in the disaggregate analysis
Conclusions
Significant reduction (17.5percent) in rear-end crashes in South Carolina
Strategy is more effective at lower volumes on the minor approaches
Urban versus rural – Strategy tended to be more effective at:
Rural installations in Connecticut Urban installations in South Carolina
Conclusions
Strategy was more effective at 3-legged intersections
No detectable effects for nighttime crashes Strategy has potential to reduce crashes cost-
effectively, particularly in situations identified
QUESTIONS???