# Presentation: 693634

## Low Cost Safety Improvements Pooled Funds StudyIncreasing Retroreflectivity of STOP Signs Results

- Low Cost Safety Improvements Pooled Funds StudyIncreasing Retroreflectivity of STOP Signs Results

**Dr. Bhagwant Persaud, Persaud and Lyon, 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

**Notes:**
Notes: 
Introduction includes Background on Strategy and Literature Review
Results include Aggregate Analysis and Disaggregate Analysis

## Background on Strategy 

- Identified by TAC, not in Guides
- Low-cost, short-term implementation
- Target crashes
- Right-angle
- Other STOP sign violation

**Notes:**
Picture. A relative visual comparison of STOP signs with six different grades of retroreflective sheeting. Type VII, VIII, IX at the top row and  I, II and III at the bottom row. Type I and II are commonly known as Engineering Grade, and Super-Engineering Grade respectively, and are both made with glass beads compositions. Types III and higher use prism technology and are generally identified as high-intensity sheeting. Brightness is shown to decrease as sign type sign type increases, i.e. Type IX is brighter than Type I. 

## 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

**Notes:**
Figure. Shows 50 States of America with Connecticut and South Carolina shaded red to indicate data were obtained from these States.

## 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 |

**Notes:**
Note that the mean values are presented in the table.  

## 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 |

**Notes:**
Note that the mean values are presented in the table.  

## 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 |

**Notes:**
The cell containing the percent reduction of 17.5 for rear-end crashes in South Carolina is shaded to emphasize a statistically significant result at the 95% confidence level.  This is the only cell in the table that is shaded (i.e. the only results from the aggregate analysis that is statistically significant at the 95% confidence level).  

Note a negative sign indicates an increase in crashes.  

## 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
 |

**Notes:**
The cell containing the standard error of 7.3 for rear-end crashes in South Carolina is shaded to emphasize a statistically significant result at the 95% confidence level. This is the only cell in the table that is shaded (i.e. the only results from the aggregate analysis that is statistically significant at the 95% confidence level).  

## Disaggregate Evaluation Results: Urban versus Rural 

| Disaggregate Group | Sites | Percent reduction of 
all crashes |
| --- | --- | --- |
| SC urban | 47 | 13.7 |
| SC rural | 61 | -2.0 |
| CT urban | 190 | -2.2 |
| CT rural | 41 | 15.4 |

- Disaggregate Evaluation Results: Urban versus Rural

**Notes:**
The cell containing the percent reduction of 13.7 for crashes at urban locations in South Carolina is shaded to emphasize a statistically significant result at the 95% confidence level. This is the only cell in the table that is shaded (i.e. the only results from the aggregate analysis that is statistically significant at the 95% confidence level).  

## Disaggregate Evaluation Results 3-leg versus 4-leg 

| Disaggregate Group | Sites | Percent reduction |
| --- | --- | --- |
| CT 3-legged | 172 | 4.1 |
| CT 4-legged | 59 | -11.6 |
| CT 3-legged, rural | 29 | 23.1 |
| CT 4-legged, rural | 12 | -0.2 |
| SC 3-legged | 48 | 15.9 |
| SC 4-legged | 60 | -5.3 |
| SC 3-legged, urban | 20 | 26.3 |
| SC 4-legged, urban | 27 | 0.05 |

- Disaggregate Evaluation Results 3-leg versus 4-leg

**Notes:**
There are 3 cells that are shaded to indicate a statistically significant reduction in crashes at the 95 percent confidence level.
CT 3-legged, rural locations had a 23.1 percent reduction, SC 3-legged locations had a 15.9 percent reduction and SC 3-legged, urban locations had a 26.3 percent reduction. 

## Disaggregate Evaluation: Effect of Minor ADT 

| Disaggregate Group | Sites | Percent reduction |
| --- | --- | --- |
| SC < 1200 minor AADT | 42 | 24.9 |
| SC > 1200 minor AADT | 66 | -3.4 |
| CT < 1000 minor AADT | 90 | 14.3 |
| CT >1000 minor AADT | 141 | -5.1 |

- Disaggregate Evaluation: Effect of Minor ADT

**Notes:**
There are 2 cells that are shaded to indicate a statistically significant reduction in crashes at the 95 percent confidence level.  The shaded cells shows disaggregate groups SC less or equal to 1200 minor AADT had a 24.9 percent reduction and CT less or equal to 1000 minor AADT had a 14.3 percent reduction emphasizing the strategy effectiveness.

## 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???