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