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REPORT
This report is an archived publication and may contain dated technical, contact, and link information
Publication Number:  FHWA-HRT-16-035    Date:  June 2016
Publication Number: FHWA-HRT-16-035
Date: June 2016

 

Safety Evaluation of Intersection Conflict Warning Systems

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FOREWORD

The research documented in this report was conducted as part of the Federal Highway Administration’s (FHWA) Evaluation of Low-Cost Safety Improvements Pooled Fund Study (ELCSI-PFS). FHWA established this pooled fund study in 2005 to conduct research on the effectiveness of the safety improvements identified by the National Cooperative Highway Research Program Report 500 Guides as part of the implementation of the American Association of State Highway and Transportation Officials Strategic Highway Safety Plan. The ELCSI-PFS studies provide a crash modification factor and benefit-cost economic analysis for each of the targeted safety strategies identified as priorities by the pooled fund member States.

Intersection conflict warning systems (ICWSs), evaluated for their safety effectiveness under this study, are intended to reduce the frequency of crashes by alerting drivers to conflicting vehicle paths on adjacent approaches at unsignalized intersections. For two-lane at two-lane intersections, results showed significant reductions for total, fatal and injury, right-angle, and rear-end crashes. For four-lane at two-lane intersections, results showed significant reductions for total, fatal and injury, right-angle, and nighttime crashes. The results suggest that the ICWSs can be cost-effective safety improvements. This report will benefit roadway designers and safety planners to provide greater intersection safety.

Monique R. Evans, P.E.
Director, Office of Safety
Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

 

Technical Report Documentation Page

1. Report No.

FHWA-HRT-16-035

2. Government Accession No. 3 Recipient's Catalog No.
4. Title and Subtitle

Safety Evaluation of Intersection Conflict Warning Systems

5. Report Date

June 2016

6. Performing Organization Code
7. Author(s)

Scott Himes, Frank Gross, Kimberly Eccles, and Bhagwant Persaud

8. Performing Organization Report No.

 

9. Performing Organization Name and Address

VHB
8300 Boone Blvd., Ste. 700
Vienna, VA 22182-2626

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-13-D-00001

12. Sponsoring Agency Name and Address

U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590

13. Type of Report and Period Covered

Safety Evaluation

14. Sponsoring Agency Code

FHWA

15. Supplementary Notes

The Federal Highway Administration (FHWA) Office of Safety Research and Development managed this study under the Development of Crash Modification Factors program. The FHWA Office of Safety Research and Development Contracting Officer’s Representative was Roya Amjadi (202) 493-3383.

16. Abstract

FHWA organized a pooled fund study of 40 States to evaluate low-cost safety strategies as part of its strategic highway safety effort. One of the strategies selected for evaluation was intersection conflict warning systems (ICWSs). This strategy is intended to reduce the frequency of crashes by alerting drivers to conflicting vehicles on adjacent approaches at unsignalized intersections. Geometric, traffic, and crash data were obtained for four-legged, rural, two-way stop-controlled intersections with ICWS installations in Minnesota, Missouri, and North Carolina. To account for potential selection bias and regression-to-the-mean, an empirical Bayes before–after analysis was conducted, using reference groups of similar four-legged, rural, two-way stop-controlled intersections without ICWS installation. The analysis also controlled for changes in traffic volumes over time and time trends in crash counts unrelated to the strategy. The combined results for all States indicated statistically significant crash reductions for most crash types for two-lane at two-lane intersections and for four-lane at two-lane intersections. For two-lane at two-lane intersections, the statistically significant crash modification factors (CMFs) for total, fatal and injury, right-angle, and rear-end crashes were 0.73, 0.70, 0.80, and 0.43, respectively. For four-lane at two-lane intersections, the statistically significant CMFs for total, fatal and injury, right-angle, and nighttime crashes were 0.83, 0.80, 0.85, and 0.61, respectively. The benefit-cost ratio estimated with conservative cost and service life assumptions was 27:1 for all two-lane at two-lane intersections and 10:1 for four-lane at two-lane intersections. The results suggest that the ICWS strategy, even with conservative assumptions on cost, service life, and the value of a statistical life, can be cost effective. Because this is an evolving strategy, the results of this study reflect installation practices to date.

17. Key Words

Intersection conflict warnings; Low-cost, Safety improvements, Safety evaluations, Empirical Bayesian

18. Distribution Statement

No restrictions. This document is available through the National Technical Information Service, Springfield, VA 22161. http://www.ntis.gov/about/contact.aspx

19. Security Classification
(of this report)

Unclassified

20. Security Classification
(of this page)

Unclassified

21. No. of Pages

76

22. Price
Form DOT F 1700.7 Reproduction of completed page authorized

SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

List of Figures

List of Tables

List of Abbreviations

AADT average annual daily traffic
B/C benefit-cost
CAS collision avoidance system
CICAS Cooperative Intersection Collision Avoidance System
CMF crash modification factor
EB empirical Bayes
FHWA Federal Highway Administration
ICAS intersection collision avoidance system
ICWS intersection conflict warning system
KABCO Scale used to represent injury severity in crash reporting (K is fatal injury, A is incapacitating injury, B is non-incapacitating injury, C is possible injury, O is property damage only)
LED light-emitting diode
MnDOT Minnesota Department of Transportation
MoDOT Missouri Department of Transportation
MUTCD Manual on Uniform Traffic Control Devices
NCDOT North Carolina Department of Transportation
NHTSA National Highway Traffic Safety Administration
PDO property damage only
PRT perception-response time
RICWS rural intersection conflict warning system
RTM regression-to-the-mean
SPF safety performance function
USDOT U.S. Department of Transportation
VEWF vehicle entering when flashing

 

 

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