low cost safety improvements pooled funds study safety evaluation of stop ahead pavement markings
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Low Cost Safety Improvements Pooled Funds Study Safety Evaluation of STOP AHEAD Pavement Markings. Dr. Frank Gross, Vanasse Hangen Brustlin (VHB), Inc. Overview. Introduction Objective Study Design Data Collection Results Economic Analysis Conclusions. Background on Strategy. STOP AHEAD - PowerPoint PPT PresentationTRANSCRIPT
Low Cost Safety Improvements Pooled Funds Study
Safety Evaluation of STOP AHEAD Pavement Markings
Dr. Frank Gross, Vanasse Hangen Brustlin (VHB), Inc
Overview Introduction Objective Study Design Data Collection Results Economic Analysis Conclusions
Background on Strategy STOP AHEAD
Tried Low cost Short-term implementation
Target crashes Right-angle Rear-end Other STOP sign violation
crashes Potential Difficulties
Visibility in winter Low coefficient of friction
Key to Success Maintenance of markings
Literature Review
STOP AHEAD pavement markings No available literature
STOP AHEAD signs Several studies Not particularly effective (Zwahlen, 1988)
Objective Estimate Safety Effectiveness
Total crash frequency Target crash frequency
• Right-angle collisions• Rear-end collisions• Injury collisions
Questions of Interest Do effects vary by:
• Traffic volumes?• Area type?• Number of approach legs?• Number of stop-controlled approaches?
Is the treatment economically feasible?
Study Design Required Sample Size
Minimum: 53 intersection-years• Detect 20 percent reduction in total crashes with 90 percent
confidence Desirable: 260 intersection-years
• Detect 10 percent reduction in total crashes with 90 percent confidence
Assumptions Number of reference sites = number of strategy sites
Data Collection
Data Collection – ArkansasTotal number of intersections used = 8
Variable Mean Minimum Maximum
Months before 102.9 82.3 127.3
Months after 32.1 16.7 49.7
Crashes/site-year before 1.60 0.13 7.78
Crashes/site-year after 1.36 0.00 9.00
Injury crashes/site-year before 0.86 0.00 4.44
Injury crashes/site-year after 1.08 0.00 7.50
Right-angle crashes/site-year before 0.82 0.00 5.00
Right-angle crashes/site-year after 0.81 0.00 6.50
Rear-end crashes/site-year before 0.32 0.00 1.78
Rear-end crashes/site-year after 0.04 0.00 0.34
Total Entering AADT before 5,330 407 11,284
Total Entering AADT after 5,588 513 11,850
Data Collection – MarylandTotal number of intersections used = 9
Variable Mean Minimum Maximum
Months before 79.0 44.7 107.9
Months after 41.0 12.1 75.3
Crashes/site-year before 3.71 0.22 7.19
Crashes/site-year after 2.83 0.00 7.00
Injury crashes/site-year before 2.18 0.11 4.29
Injury crashes/site-year after 1.34 0.00 3.20
Right-angle crashes/site-year before 1.49 0.00 3.81
Right-angle crashes/site-year after 1.06 0.00 3.60
Rear-end crashes/site-year before 0.58 0.00 1.68
Rear-end crashes/site-year after 0.59 0.00 2.00
Total Entering AADT before 8,094 1,627 14,043
Total Entering AADT after 8,856 1,663 17,263
Data Collection – MinnesotaTotal number of intersections used = 158
Variable Mean Minimum Maximum
Months before 117.0 36.0 120.0
Months after 26.1 24.0 96.0Crashes/site-year before 0.04 0.00 0.67
Crashes/site-year after 0.01 0.00 0.63
Injury crashes/site-year before 0.02 0.00 0.40
Injury crashes/site-year after 0.00 0.00 0.20
Right-angle crashes/site-year before 0.01 0.00 0.30
Right-angle crashes/site-year after 0.00 0.00 0.33
Rear-end crashes/site-year before 0.00 0.00 0.10Rear-end crashes/site-year after 0.00 0.00 0.17
Total Entering AADT before 756 80 6,076
Total Entering AADT after 858 88 6,310
Evaluation Results
States
Percent reduction in Right-angle
crashes
Percent reduction in
Rear-end crashes
Percent reduction in
Injury crashes
Percent reduction in Total crashes
Combined Results(AR and MD) -3.6 29.0 21.6 31.1
AR Results 42.1 90.3 31.7 52.3
MD Results -39.0 -1.6 17.6 22.9
MN Results 66.9 67.9 82.2 34.1
Note: A negative sign indicates an increase in crashes.Bold numbers indicate a statistically significant effect (95% confidence level).
Aggregate Analysis
Evaluation Results
StatesStandard Error
for Right-angle crashes
Standard Error for Rear-end crashes
Standard Error for Injury crashes
Standard Error for
Total crashes
Combined Results(AR and MD) (18.1) (18.0) (12.0) (8.0)
AR Results (17.5) (9.5) (18.1) (10.8)
MD Results (31.1) (28.7) (15.4) (10.5)
MN Results (23.4) (32.1) (12.6) (19.3)
Note: A negative sign indicates an increase in crashes.Bold numbers indicate a statistically significant effect (95 percent confidence level).
Aggregate Analysis
Evaluation ResultsDisaggregate Analysis
Note: A negative sign indicates an increase in crashes.Bold numbers indicate a statistically significant effect (95% confidence level).
Disaggregate Group Sites Estimate of Percent Reduction(standard error)
Injury crashes:3-legged 5 54.7 (16.4)
Injury crashes:4-legged 12 11.9 (15.0)
Injury crashes: All-way stop-controlled 7 42.3 (14.9)
Injury crashes: All-way stop-controlled/ Two-way stop-controlled 10 7.7 (17.5)
Total crashes:3-legged 5 60.1 (11.2)
Total crashes: 4-legged 12 23.0 (9.9)
Total crashes: All-way stop-controlled 7 55.9 (9.1)
Total crashes: All-way stop-controlled/ Two-way stop-controlled
10 12.8(12.2)
Economic Analysis
Determine the Annual Cost of Installation States Provided Installation Costs and Service Life
Latex: $140 per approach (2 year service life) Thermoplastic: $1,500 per approach (5 year service life)
Convert Installation Cost to Annual Cost
Latex: $78 per approach/year Thermoplastic: $366 per approach/year
N -R)(1-1R*CCost Annual
Economic AnalysisEstimate Crash Costs FHWA Unit Crash Cost Data (Council et al., 2005)
$58,832 for undefined collision Includes “hard dollar” and “non-monetary” costs
Assume 2:1 Benefit-Cost Ratio
Required Crash Reduction (2:1 Benefit-Cost Ratio) Latex: 0.005 (Two-way stop- controlled) or 0.011 (All-way
stop- controlled) Thermoplastic: 0.025 (Two-way stop- controlled) or 0.050
(All-way stop- controlled)
CostCrash Unit onsInstallati*Cost Annual*2Reduction Required
Conclusions
Total Crashes Significant reduction in AR, MD, and overall
Right-angle and Rear-end Crashes Significant reduction in AR
Injury Crashes Significant at 10 percent level overall
Disaggregate Analysis Greater effect for 3-legged (highly significant) Greater effect for All-way stop-controlled (highly
significant) Some variation by AADT
Conclusions General Reduction in Crashes
Results supported by MN data
Economically Feasible Low cost strategy Modest reduction to achieve 2:1 Benefit-Cost ratio Necessary reduction is easily achievable
CRASHES
Benefit >> Cost
QUESTIONSor
COMMENTS