Design Guidelines for Raised and Traversable Medians in Urban Areas

About the report:

Major urban and suburban streets must provide a high level of service for through traffic as well as access to abutting properties. To an extent, the provisions of traffic service and the accommodation of access needs are conflicting functions that are affected through different treatments of the median. The regulation of left-turn traffic through the utilization of alternate median controls is a primary method of expediting through traffic and providing adequate access to adjacent development. Although several investigators have examined the merits of raised medians with barrier curbs and traversable or continuous two-way, left-turn median lanes, guidelines for selecting the treatment best suited for particular roadway and traffic conditions have not been fully developed. The absence of guidelines has led to considerable differences in opinion among planners, designers, and traffic engineers concerning the selection of an appropriate median treatment. Often the design chosen has generated criticism from the motoring public, property owners, and businessmen. An inappropriate design can also lead to safety and operational problems as well as the ineffective use of highway revenue. The scope of the research reported here included a literature review, a questionnaire survey of design engineers in major U. S. cities and state departments of transportation, and the collection of traffic, land use, and accident data covering a three-year period for 50 urban and suburban roadways in Virginia. Data were also collected on four-lane undivided sites to provide a basis for examining the effects of alternative median controls. Analysis of variance and multiple linear regression techniques were employed to identify and quantify the safety and operational impacts of alternative median treatments. Based on the results of the analysis and on the information obtained from the survey of current practices, a set of guidelines was developed for selecting appropriate median controls. The guidelines are intended to assist in the choice of a specific median design by providing an assessment of the impacts of the various treatments under existing as well as future land use, traffic, and operational conditions. The guidelines include quantitative as well as subjective factors which provide a rational basis for aiding the decision maker in selecting a particular design.

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