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3CHAPTER 1 INTRODUCTION BACKGROUND Many state and local transportation agencies are consider- ing installing nontraversable medians on multilane arterial highways to improve safety and travel times. Business and property owners often resist such improvements because they and their customers may be denied the opportunity for direct left-turn access to or from their property. Traffic destined for such locations must use alternate routes, some of which may involve making U-turns at nearby median openings. Figure 1 illustrates drivers making U-turn maneuvers at an unsignalized median opening. It is often inconvenient for those denied direct left-turn access to use alternative routes to reach their destination, and the additional travel distance or time for using an alter- native route may cause some delay that should be consid- ered in the decision to implement the project. An argument has been advanced by some opponents of projects that restrict direct left-turn access that any increase in U-turns may pose a safety problem, potentially offsetting the antic- ipated safety benefits of restricting direct left-turn access. However, highway agencies currently are not able to respond to such arguments because the safety effects of increased U-turn volumes are largely unknown. Most before-after safety evaluations of projects involving median installation have focused on the effect of the median on safety within the proj- ect limits while, because of the alternative routes used by motorists to reach their destinations, some of the traffic and some of the accidents may have moved beyond the project limits. Another concern of highway agencies is that, after a non- traversable median has been installed, highway agencies are often approached by property owners requesting that a median opening be installed to provide direct left-turn access to and from their property. Currently, highway agencies are unable to make such decisions on a sound engineering basis because they lack the necessary tools to evaluate the safety and operational effects of providing new median openings. There are median opening designs that might satisfy a prop- erty owner without unduly affecting the safety and traffic operations of a road, such as openings that permit left-turn maneuvers into a driveway, but prohibit left turns out of the driveway. However, there is little documentation of the safety and traffic operational effects of such designs. RESEARCH OBJECTIVES AND SCOPE The objectives of the research are as follows: ⢠To document the safety performance of median open- ings of various designs; ⢠To determine the safety and operational effects of U-turns at median openings; and ⢠To develop a guide for the use, location, and design of unsignalized median openings for U-turns. The scope of the research includes median openings on all types of divided highways. However, although median open- ings on rural divided highways have been included, the focus of the research is on median openings on urban/suburban arterials because these present the greatest current challenge to highway agencies in access management. The research scope is limited to unsignalized median openings in urban/suburban areas. Thus, the guidelines are specifically applicable to median openings without traffic signals. ORGANIZATION OF THIS REPORT This report presents the results of the literature review, the survey of highway agencies, a classification of typical median opening designs, a description of the data collection and analy- sis efforts, the results of the analyses, and conclusions and recommendations. The remainder of this report is organized as follows. Chap- ter 2 summarizes current knowledge on the safety and oper- ation of U-turns at unsignalized median openings. Current design policies and practices of state and local highway agen- cies related to median openings at unsignalized intersections are presented in Chapter 3. Chapter 4 presents a classification
4of typical median opening designs used to accommodate U- turn maneuvers at unsignalized locations. The factors used in the classification process and the factors that influence the safety and operational performance of median openings are also identified in Chapter 4. The data collection and analyses are described in Chapter 5. The results of the analyses are presented in Chapter 6. Chapter 7 presents the conclusions and recommendations. Appendix A presents the survey questionnaire distributed to state and local highway agencies concerning median open- ings at unsignalized intersections. Appendix B summarizes the highway agency responses to the survey questionnaire. Appendix C presents guidelines for the use, location, and design of unsignalized median openings. Figure 1. U-turn maneuvers at unsignalized median opening.
