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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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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.
