Low Cost Safety Improvements Pooled Funds Study Safety Evaluation of STOP AHEAD Pavement Markings

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



Months after 41.0 12.1 75.3

Crashes/site-year before 3.71 0.22 7.19






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



Months after 26.1 24.0 96.0Crashes/site-year before 0.04 0.00 0.67






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

Low Cost Safety Improvements Pooled Funds Study Safety Evaluation of STOP AHEAD Pavement Markings

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