# Presentation: 746276

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

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

- Dr. Frank Gross, Vanasse Hangen Brustlin (VHB), Inc

**Notes:**
Cover page pictures. Picture shows series of three scenarios: a vehicle on a meandering road, safety personnel at work, and a car that is very badly damaged after it appears to have collided into a telephone pole.  

## 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

**Notes:**
Picture: STOP AHEAD pavement marking in conjunction with a STOP AHEAD sign. 

Notes: 
STOP AHEAD pavement markings were identified in the NCHRP 500 Series as a tried strategy.
This strategy is low-cost ($150 latex and $750 thermoplastic per approach) and has a short-term implementation time frame (3 months or less).
Target crash types include:
Right-angle, rear-end, and other crashes associated with STOP sign violation.
The strategy is used to increase driver-awareness of the stop sign on a stop-controlled approach.
Potential Difficulties
Visibility is critical to this strategy and snow and debris could greatly influence the effectiveness.
Another potential drawback is that the pavement marking may have a relatively low coefficient of friction compared to other areas on the approach.
The key to success is the continued maintenance of the pavement markings.
Service life is relatively short (less than 5 years).

## Literature Review

- STOP AHEAD pavement markings
- No available literature
- STOP AHEAD signs
- Several studies
- Not particularly effective (Zwahlen, 1988)

**Notes:**
Picture: Stop Ahead sign: diamond-shaped sign with yellow background with black wording STOP AHEAD 

Notes: 
The safety effectiveness of STOP AHEAD pavement markings has not been adequately quantified.
The Study team did not uncover any safety studies related to STOP AHEAD pavement markings.
Several studies have been conducted to evaluate STOP AHEAD signs
Results indicated that the signs are not particularly effective in reducing crashes
Roadside vegetation is also a potential problem for roadside signs. 

## 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?

**Notes:**
Notes: 
The objective of this study is to estimate the safety effectiveness of STOP AHEAD pavement markings.
The measures of effectiveness are total crash frequency and target crash frequency.
Target crashes included right-angle, rear-end, and injury crashes.
Specific questions to be answered are as follows:
Do effects vary by traffic volumes?
Do effects vary by area type?
Do effects vary by number of approach legs?
Do effects vary by number of stop-controlled approaches?
Is the treatment economically feasible?
A disaggregate analysis was completed to address the first 4 questions and an economic analysis was conducted to determine the potential economic impacts.

## 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

**Notes:**
Notes: 
Sample size calculations were based on the assumption of a before-after study with comparison group.
We determined that 53 intersection-years are required to detect a 20 percent reduction in total crashes with 90 percent confidence
However, it was desirable to be able to detect a 10 percent reduction in total crashes with 90 percent confidence.
This would require 260 intersection-years
Assumptions
Before-after with reference group
Number of reference sites = number of strategy sites

## Data Collection

**Notes:**
Figure: Shows 50 States of America with Arkansas, Maryland and Minnesota shaded brown to indicate data were obtained from these States.

## Data Collection – Arkansas

- Total 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 |

**Notes:**
Notes: 
There were a total of 8 strategy sites identified in Arkansas.
11 years of data were collected for AR (1994-2004) with an average of 103 months before and 32 months after implementation.
Total and rear-end crashes per site year appear to decrease from the before to the after period despite an increase in AADT.
Injury crashes appear to increase slightly while right angle crashes remain the same.

## Data Collection – Maryland

- Total 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 |

**Notes:**
Notes: 
There were a total of 9 strategy sites identified in Maryland.
10 years of data were collected for MD (1996-2005) with an average of 79 months before and 41 months after implementation.
Total, injury, and right-angle crashes appear to decrease from the before to the after period despite an increase in AADT.
Rear-end crashes remain the same.

## Data Collection – Minnesota

- Total number of intersections used = 158

| Variable | Mean | Minimum | Maximum |
| --- | --- | --- | --- |
| Months before | 117.0 | 36.0 | 120.0 |
| Months after | 26.1 | 24.0 | 96.0 |
| Crashes/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 | 0.10 |
| Rear-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 |

**Notes:**
Notes: 
There were a total of 158 strategy sites identified in Minnesota.
11 years of data were collected for MN (1995-2005) with an average of 117 months before and 26 months after implementation.
Crash rates for MN are substantially different than those from the other 2 States; however, AADT is also much lower.
Total, injury, and right-angle crashes appear to decrease from the before to the after period despite an increase in AADT.
Rear-end crashes remain the same.

## 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

**Notes:**
There are cells which the numbers are bolded to indicate that the results are statistically significant at the 95 percent confidence level. The numbers are bolded for the following:
Percent reduction in total crashes for the combined results from AR and MD;
Percent reduction in angle crashes, rear-end, and total crashes for Arkansas;
Percent reduction in total crashes for Maryland; and
Percent reduction in angle crashes, rear-end crashes, and injury crashes for Minnesota.

Notes: 
The primary analysis focused on AR and MD; MN was excluded from the combined model because of the unusually low crash rates.
For AR, MD, and the combined model, the results show a consistent reduction in total and injury crashes.
The reductions in total crashes are all highly significant (5 percent significance level).
For the target crashes (right-angle and rear-end), there was a significant reduction shown for AR.
The MN results support the conclusions drawn from the other 2 States and show a consistent reduction in all categories.

## Evaluation Results

| States | Standard 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

**Notes:**
There are cells which the numbers are bolded to indicate that the results are statistically significant at the 95 percent confidence level. The numbers are bolded for the following:
Percent reduction in total crashes for the combined results from AR and MD;
Percent reduction in angle crashes, rear-end, and total crashes for Arkansas;
Percent reduction in total crashes for Maryland; and
Percent reduction in angle crashes, rear-end crashes, and injury crashes for Minnesota.

Notes:
The primary analysis focused on AR and MD; MN was excluded from the combined model because of the unusually low crash rates.
For AR, MD, and the combined model, the results show a consistent reduction in total and injury crashes.
The reductions in total crashes are all highly significant (5 percent significance level).
For the target crashes (right-angle and rear-end), there was a significant reduction shown for AR.
The MN results support the conclusions drawn from the other 2 States and show a consistent reduction in all categories.

## Evaluation Results

- Disaggregate 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) |

**Notes:**
There are cells which the numbers are bolded to indicate that the results are statistically significant at the 95 percent confidence level. The numbers are bolded for the following:
3-legged injury crashes, All-way stop-controlled injury crashes, 3-legged total crashes, 4-legged total crashes and all-way stop-controlled total crashes. 

Notes:  
The disaggregate analysis focused on the combined data from AR and MD.
Only total and injury crashes were able to be included due to small sample issues in the other 2 crash categories.
For the disaggregate analysis, there is a reduction in crashes for both 3- and 4-leg intersections, but the reduction is significantly greater for the 3-leg intersections.
Results are similar for the type of stop control. Both All Way Stop Control and those intersections without All Way Stop Control show a reduction in crashes after installation of STOP AHEAD markings, but the reductions are significantly greater for All-way stop-controlled intersections.

## 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

**Notes:**
Equation. Annual Cost. Annual cost equals installation cost multiplied by discounted rate, that product divided by 1 minus bracket opened 1 plus discounted rate bracket closed raised to the power negative number of years

Notes: 
An economic evaluation was performed to determine the cost effectiveness of STOP AHEAD pavement markings.
The States were asked to provide installation and maintenance costs as well as the expected service life of the installation.
Conservative estimates were used for the cost and service life.
There were 2 types of pavement markings identified: Latex and Thermoplastic
The total costs were converted into annual costs

## Economic Analysis

- Estimate 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)

**Notes:**
Equation: Required reduction. Required reduction equals 2 multiplied by annual cost multiplied by installations, that product divided by unit crash cost

Notes: 
Crash costs were obtained from FHWA’s most recent unit crash cost data
The results focus on total crashes
$58,832 was used as the cost of an average (unknown) crash type
The required reductions to achieve a 2:1 benefit-cost ratio are shown for different stop-control configurations.

## 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

**Notes:**
Notes: 
To reiterate the results:
A significant reduction in total crashes was shown for AR, MD, and the combined model.
A significant reduction in right-angle and rear-end crashes was shown for AR
A consistent reduction in injury crashes was shown across the States, but only the results for the combined model were significant (at the 10 percent significance level).
The disaggregate analysis revealed that the reductions were not constant.
Reductions were greater for 3-leg intersections, All Way Stop Control intersections, and some variation was identified across AADT levels, but this last finding was not conclusive. 

## 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

- Benefit >> Cost

**Notes:**
Figure: Shows an arrow with green background pointing down with CRASHES written in it. This means general reduction of crashes

In general, the analysis indicated a reduction in crashes after the installation of STOP AHEAD pavement markings.
The MN results were not included in the combined analysis, but supported the general findings.
The economic analysis was also supportive of this strategy
First, this strategy is very low cost, which means that modest reductions in crashes will justify its use.
Based on the crash analysis, these modest reductions are easily achievable.

## QUESTIONS
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