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Journal Article

Citation

Harwood DW, Pietrucha M, Fitzpatrick K, Wooldridge M. Transp. Res. Circular 1998; (E-C003): 29:1-14.

Copyright

(Copyright © 1998, U.S. National Academy of Sciences Transportation Research Board)

DOI

unavailable

PMID

unavailable

Abstract

Current design policies used in the United States do not provide clear guidance on the effect of median width on the traffic operations and safety of at-grade intersections on multilane divided highways. This paper examines the relationship of the median width and median opening length to intersection operations and safety by means of accident analyses, field observational studies, and traffic operational modeling. The research results indicate that at rural unsignalized intersections, the frequency of both accidents and undesirable driving behavior decreases as the median width increases. Conversely, at suburban unsignalized intersections, the frequency of accidents and undesirable driving behavior increases with increasing median width. Delay at signalized intersections also increases with increasing median width. Based on these results, the paper provides guidance on the selection of appropriate median widths for signalized and unsignalized intersections on divided highways in rural and suburban areas. Multilane divided cross sections are frequently used by highway agencies for major nonfreeway facilities in rural and suburban areas. The multilane cross section enables the highway to operate between intersections with a capacity (under ideal conditions) approaching that of a freeway. The presence of a median provides a physical separation between the vehicles traveling in opposite directions and reduces accident rates below the levels found on undivided highways. At-grade intersections represent one of the major sources of traffic operational and safety problems on multilane divided highways. Turning volumes are generally larger at intersections than at driveways and midblock median openings, and accidents tend to cluster at locations where the turning volumes are highest. This paper examines the effect of two key geometric design parameters - median width and median opening length - on the operations and safety of divided highway intersections. Both signalized and unsignalized intersections are considered.

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