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Publication Number:  FHWA-HRT-17-082    Date:  December 2017
Publication Number: FHWA-HRT-17-082
Date: December 2017

 

Safety Evaluation of Signalized Restricted Crossing U-Turn Intersections

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FOREWORD

The research documented in this report was conducted as part of the Federal Highway Administration’s (FHWA’s) 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 (AASHTO) 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.

A restricted crossing U-turn (RCUT) intersection is defined as a three- or four-approach intersection where minor street left-turn and through movements (if any) are rerouted to one-way downstream U-turn crossovers. This study collected and analyzed crash data before and after conversion of 11 intersections from conventional to RCUT design. The intersections were in suburban areas on four- or six-lane arterials. Study results show a signalized RCUT to be effective to reduce total crashes, and reduce injury crashes since they generally reduce the more severe angle and turning crashes. The study estimated B/C ratio for installing an RCUT shows that this strategy, when considering safety and operations, is cost beneficial. This report is intended for safety engineers, highway designers, planners, and practitioners at State and local agencies involved with AASHTO Strategic Highway Safety Plan implementation.

Jonathan Porter, Ph.D.
Acting Director, Office of Safety
Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation (USDOT) 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-17-082

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

Safety Evaluation of Signalized Restricted Crossing U-Turn Intersections

5. Report Date

December 2017

6. Performing Organization Code
7. Author(s)

Joseph E. Hummer, Ph.D., P.E., and Sathish Rao

8. Performing Organization Report No.

 

9. Performing Organization Name and Address

VHB
8300 Boone Blvd., Ste. 700
Vienna, VA 22182-2626
Wayne State University
Department of Civil and Environmental Engineering
Detroit, MI 48202

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-13-D-00001

12. Sponsoring Agency Name and Address

Federal Highway Administration
Office of Safety Research and Development
6300 Georgetown Pike
McLean, VA 22101-2296

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 (DCMF) program. The FHWA Office of Safety Research and Development Program and Task Manager was Roya Amjadi (HRDS-20).

16. Abstract

This study evaluated restricted crossing U-turn (RCUT) intersection and was conducted by the DCMF program for the Evaluation of Low-Cost Safety Improvements Pooled Fund Study. RCUT is defined as a three-approach or four-approach intersection where minor street left-turn and through movements (if any) are rerouted to one-way downstream U-turn crossovers. RCUTs are also known as superstreets, J-turns, reduced conflict intersections, and synchronized streets. Previous research has shown that unsignalized RCUTs are generally safer than conventional options. However, there are no known studies specific to the safety of signalized RCUTs. The objective of this effort was to collect and analyze crash data to develop a crash modification factor (CMF) for signalized RCUTs.

This study collected and analyzed crash data before and after conversion of 11 intersections from conventional to RCUT design. The intersections were in suburban areas on four- or six-lane arterials. For most individual sites and groups of sites examined, odds ratio tests showed that there were high-quality comparison sites available, and regression to the mean was not an issue. The project team recommends a CMF of 0.85 for overall crashes and 0.78 for injury crashes for the conversion of a conventional intersection to an RCUT intersection.

Based on those CMFs, the project team produced an estimated benefit-to-cost ratio of 3.6 to 1.0 when considering safety and operations or 2.6 to 1.0 considering safety only.

17. Key Words

RCUT, restricted crossing U-turn, superstreet, J-turn, synchronized street, signalized, safety, CMF

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)

 

20. Security Classification
(of this page)

 

21. No. of Pages

70

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

SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

LIST OF FIGURES

LIST OF TABLES

LIST OF ABBREVIATIONS

B/C benefit–cost
CMF crash modification factor
CRF crash reduction factor
DCMF Development of Crash Modification Factors (program)
EB empirical Bayesian
FHWA Federal Highway Administration
RCUT restricted crossing U-turn

EXECUTIVE SUMMARY

A restricted crossing U-turn (RCUT) intersection is defined as a three-approach or four-approach intersection where minor street left-turn and through movements (if any) are rerouted to one-way downstream U-turn crossovers. RCUTs are also known as superstreets, J-turns, reduced conflict intersections, and synchronized streets. Ten States have installed at least 50 RCUTs since the late 1980s. At least five States have installed signalized RCUTs—those at which the major street crossover(s) and U-turn crossover(s) are under the control of traffic signals. Studies have shown RCUTs to have advantages over traditional intersections in terms of travel time and delay, signal progression, pedestrian crossing, and transit service.

While there are theoretical reasons that support the relative safety benefits of RCUTs as compared to conventional intersections, it is also possible that certain RCUT elements could diminish or negate these benefits. For example, signalized RCUTs involve a greater number of signals at the U-turn crossover(s) and require that some users travel longer overall distances. There is no known completed research on the safety of signalized RCUTs.

The objective of this evaluation was to develop a crash modification factor (CMF) for the replacement of a traditional signalized intersection with a signalized RCUT. The project team also intended for the evaluation to conduct a qualitative analysis of crash data at signalized RCUTs to provide information to designers on expected crash patterns and trends. Finally, the research team developed a benefit–cost (B/C) ratio.

The project team selected the before–after analysis with comparison sites methodology for this evaluation. The method accounts for simultaneous event biases, which the project team thought to be the most threatening potential bias to the evaluation. Simultaneous event biases that could have been important include the recession of the late 2000s and development in the area of the study sites. An empirical Bayesian methodology was unnecessary in this case because regression to the mean was not a serious threat to the validity of the analysis. The method relies on high-quality comparison sites, and the quality of the comparison sites is testable. The project team collected data from 11 treatment sites in 4 States: Alabama, North Carolina, Ohio, and Texas. The treatment sites were all in suburban areas, on four-lane or six-lane divided arterials, and characterized by high-speed traffic and minimal crossing pedestrians. The project team analyzed four potential comparison sites per treatment site. In addition to the before–after analyses of all reported crashes, the project team conducted a before–after analysis of fatal and injury crashes.

The research resulted in estimated CMFs of 0.85 for overall crashes and 0.78 for injury crashes. These CMFs are not statistically significant at the 95- or 90-percent confidence level. The injury CMF is significantly different from 1.0 at the 68-percent confidence interval. This is the first effort to develop a CMF for this strategy. Future evaluations can expand the sample size and use more robust methods that may result in CMFs with higher confidence. The CMFs suggest that signalized RCUTs will generally produce a crash reduction.

Economic analysis resulted in an estimated total annualized RCUT cost of $369,000. The estimated costs included costs for construction and signal operation and maintenance. The estimated benefits included savings of travel time and crashes. The 11 RCUTs were estimated to save 103 hours of motorist time per workday, which equates to $388,000 per year. The safety benefit was a savings of 3.0 property-damage-only crashes per year and 2.3 injury and fatal crashes per year, which results in an annual monetary savings of $948,000. Thus, the B/C ratio was 2.6 to 1.0 considering the safety benefits only and 3.6 to 1.0 considering the combined safety and operational benefits.

 

 

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