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REPORT
This report is an archived publication and may contain dated technical, contact, and link information
Publication Number:  FHWA-HRT-16-036    Date:  April 2016
Publication Number: FHWA-HRT-16-036
Date: April 2016

 

Safety Evaluation of Continuous Green T Intersections

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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 PFS 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 (B/C) economic analysis for each of the targeted safety strategies identified as priorities by the pooled fund member States.

This study compares the safety performance of the continuous green T (CGT) intersections with conventional signalized T intersections using treatment and comparison sites from Florida and South Carolina. The results show crashes were reduced for expected total, fatal and injury, and target (rear-end, angle, and sideswipe) crashes at the CGT intersection compared with the conventional signalized T intersection. Further, the B/C analysis indicated that the CGT intersection is a cost-effective alternative to the traditional, signalized T intersection. This report is intended for practicing engineers when contemplating application of CGT intersections and for researchers who wish to consider the propensity scores-potential outcomes framework in non-randomized, observational traffic safety evaluations.

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-16-036

2. Government Accession No.

 

3 Recipient's Catalog No.

 

4. Title and Subtitle

Safety Evaluation of Continuous Green T Intersections

5. Report Date

April 2016

6. Performing Organization Code

 

7. Author(s)

Donnell, Eric; Wood, Jonathan; and Eccles, Kimberly

8. Performing Organization Report No.

 

9. Performing Organization Name and Address

VHB
8300 Boone Blvd., Ste. 700
Vienna, VA 22182-2626
Penn State University
212 Sackett Building
University Park, PA 16802 3R7

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. The FHWA Office of Safety Research and Development Contracting Officer’s Representative Manager was Roya Amjadi.

16. Abstract

The continuous green T (CGT) intersection is characterized by a channelized left-turn movement from the minor street approach onto the major street, along with a continuous through movement on the major street. The continuous through movement typically has a green through arrow indicator to inform drivers that they do not have to stop. Past research has consistently shown that there are operational and environmental benefits to implementing this intersection form at three-leg locations when compared with a conventional signalized T intersection. These benefits include reduced delay, fuel consumption, and emissions. The safety effects of the conventional signalized T intersection are less clear. Past research has been limited to a small sample of intersections in a single State and considered only comparisons in reported crashes between adjacent lanes on the major street approach (continuous flow versus the opposing through lanes). The study designs used in past safety research were limited to simple statistical comparisons using reported crash data. The present study overcomes past safety research evaluations by using a propensity scores-potential outcomes framework to compare the safety performance of the CGT with conventional signalized T intersections using 30 treatment and 38 comparison sites from Florida and 16 treatment and 21 comparison sites from South Carolina. The results showed that the expected total, fatal and injury, and target crash (rear-end, angle, and sideswipe) frequencies were lower at the CGT intersection relative to the conventional signalized T intersection (CMFs of 0.958 (95 percent confidence interval (CI) = 0.772–1.189), 0.846 (95 percent CI = 0.651–1.099), and 0.920 (95 percent CI = 0.714–1.185), respectively). Further, the benefit-cost analysis indicated that the CGT intersection is a cost-effective alternative to the traditional, signalized T intersection. The results of the safety evaluation were not statistically significant, likely due to a small sample of treatments. When considered in combination with the operational and environmental benefits, the CGT intersection appears to be a viable alternative intersection form, although anecdotal feedback from South Carolina and Florida indicate that some non-motorized users (pedestrians and bicyclists) find it challenging to cross the continuous flow through lanes on the major street approach when traffic volumes limit the number or size of available gaps.

17. Key Words

Continuous green T intersection, safety performance, propensity scores, economic analysis

18. Distribution Statement

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

19. Security Classification
(of this report)

Unclassified

20. Security Classification
(of this page)

Unclassified

21. No. of Pages

81

22. Price

 

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

EXECUTIVE SUMMARY

CHAPTER 1. INTRODUCTION

CHAPTER 2. LITERATURE REVIEW

CHAPTER 3. OBJECTIVES

CHAPTER 4. METHODOLOGY

CHAPTER 5. DATA COLLECTION

CHAPTER 6. MATCHING

CHAPTER 7. CMF ESTIMATION

CHAPTER 8. ECONOMIC ANALYSIS

CHAPTER 9. SUMMARY AND CONCLUSIONS

APPENDIX A. MATCHED DATA MODELS

APPENDIX B. UNMATCHED DATA MODELS

ACKNOWLEDGEMENTS

REFERENCES

LIST OF FIGURES

LIST OF TABLES

 

LIST OF ABBREVIATIONS

AADT average annual daily traffic  
AASHTO American Association of State Highway and Transportation Officials  
B/C benefit-cost  
CDF cumulative distribution function  
CGT continuous green T  
CI confidence interval  
CMF crash modification factor  
DCMF Development of Crash Modification Factors  
EB empirical Bayes  
ELCSI-PFS Evaluation of Low-Cost Safety Improvements Pooled Fund Study  
FDOT Florida Department of Transportation  
FHWA Federal Highway Administration  
HSM Highway Safety Manual  
K-S Kolmogorov-Smirnov  
NCHRP National Cooperative Highway Research Program  
NN nearest-neighbor  
PDO property damage only  
PFS pooled fund study  
SCDOT South Carolina Department of Transportation  
SUTVA Stable Unit Treatment Value Assumption  

 

 

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