To correct the problem of interlocking left turns within bidirectional crossovers at major street intersections, directional crossovers were constructed through the the median, approximately 300 ft from the major crossroad, and some or all of the left-turning traffic was required to use the crossovers. A 4-lane divided roadway and a 60-foot median are absolute minimum requirements for such operations. If prossible, median widths of a least 72 feet are ideal because a future lane may be constructed on each side and still accommodate design vehicles. A roadway cross-section with a 48-foot median and 3 lanes in each direction will operate as well as one with a 60-foot median with two lanes in each direction. To aid motorists on the crossroad to make a left turn, the signing known as the "fish hook" was found to be the best. A careful analysis of the left-turn volumes should precede a decision as to which should be prohibited. Details are given of the redesign of an intersection. Two four-lane divided highways with 60-foot medians were analysed with each left turn routed through separate directional crossovers, and the capacity analysis showed room to spare. Some of the bidirectional crossovers between major crossroads particularly those serving major traffic generators such as shopping centers were, however, suffering from interlocking left turns. In some of the more troublesome areas, the intermediate crossovers were removed and back-to-back directional crossovers were constructed. The reconstruction is outlined of Eight-Mile Road on the outskirts of Detroit in which 2-way signal progression is possible at all times of the day. The results are discussed of a before and study of this location. Evaluation of such information for other projects leads to the conclusion that bidirectional crossovers appear to have a significant effect in reducing the number of accidents, particularly right angle accidents.

  • Corporate Authors:

    Institute of Traffic Engineers

    2029 K Street, NW
    Washington, DC    20006
  • Authors:
    • Savage, W F
  • Publication Date: 1974-8

Media Info

  • Pagination: p. 21-23
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00262428
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Dec 13 1974 12:00AM