In the early and mid 1960s the Michigan Department of Transportation (then Michigan State Highway Department) developed what is still believed to be a unique urban interchange design. This geometric configuration is an alternative to the typical tight urban diamond interchange. The configuration has many alternatives but the classic design is an interchange with a major urban arterial where the arterial is at grade and the freeway goes under. There are also parallel one-way frontage roads. The structure carrying the arterial does not have any storage lanes for left-turning traffic. Separate left-turn structures are provided to the left and right of and at a distance of 150-200 m from the cross road. The two exit and two entrance freeway ramps are located just beyond the one way left-turn structures. The operation is similar to other intersections with the Michigan indirect left turn design. Left-turning traffic desiring to enter the freeway from the crossroad turn right at the first frontage road; turn left and enter the left-turn structure; cross over the freeway; turn left onto the other frontage road; proceed along the frontage road and enter the freeway via the entrance ramp. In some cases the left-turning traffic exiting the freeway also are not allowed to turn onto the crossroad but rather use the left turn structure beyond the crossroad to complete the maneuver. It is important that the geometric design be coordinated with operation of the traffic signals. The travel time to complete the indirect left turn should be approximately one half of the cycle length of the traffic signals. Thus the left-turning traffic starting on green will arrive at the start of green of the other signal. Therefore the capacity for accommodating left turn traffic in increased greatly and the delay can actually be reduced. This geometric configuration was recently evaluated with respect to a typical tight diamond interchange and the popular single point interchange. The operation of the Michigan Urban Diamond in the presence of frontage roads far exceeds that of the single point and also that of the traditional tight diamond. Because the arterial crossroad and the frontage roads are at grade, intersection and stopping sight distances are excellent. The sight lines to the traffic signals are unobstructed. The right-of-way required for a Michigan Urban Diamond is the same as that for a tight diamond. It was found to be difficult to almost impossible to do a direct comparison of the construction costs for each configuration because they were built in different decades and often other construction (such as sewers) is included in the contracts. However, it is suggested that the cost of a Michigan Urban Diamond is approximately the same as that of a tight diamond and 60% of that of a single point. The earthwork and pavement area is about the same with the structure costs being the largest difference.

  • Supplemental Notes:
    • The publisher's German name is Forschungsgesellschaft fur Strassen- und Verkehrswesen (FGSV).
  • Corporate Authors:

    Road and Transportation Research Association

    Postbox 50 13 62
    D-50973 Cologne,   Germany 
  • Authors:
    • Maleck, T L
  • Conference:
  • Publication Date: 2000-6


  • English

Media Info

  • Features: Figures; Photos; References; Tables;
  • Pagination: p. 547-556

Subject/Index Terms

Filing Info

  • Accession Number: 00794812
  • Record Type: Publication
  • Report/Paper Numbers: FGSV 002/67
  • Files: TRIS
  • Created Date: Jun 28 2000 12:00AM