United States Department of Transportation
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Highway Capacity Manual Chapter on Alternative Intersections and Interchanges: [techbrief]
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2016-07-01
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[PDF-753.52 KB]
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Abstract:Today’s transportation professionals, with limited resources available to them, are challenged to meet the mobility needs of an increasing population. At many highway junctions, congestion continues to worsen, and drivers, pedestrians, and bicyclists experience increasing delays and heightened exposure to risk. Today’s traffic volumes and travel demands often lead to safety problems that are too complex for conventional intersection and interchange designs to properly handle. Consequently, more engineers are considering various innovative treatments as they seek solutions to these complex problems.
Highway Capacity Manual (HCM) Chapter 23, Ramp Terminals and Alternative Intersections, provides qualitative guidance and computational analysis procedures for four interchange designs and three intersection designs.(1) The original three interchange designs (i.e., the partial cloverleaf (parclo), diamond, and single-point urban interchange (SPUI) are considered conventional designs. The four new alternative designs are the diverging diamond interchange (DDI, also known as the double crossover diamond interchange), displaced left-turn (DLT) intersection, restricted crossing U-turn (RCUT) intersection, and median U-turn (MUT) intersection. These designs, which are illustrated in Figure 1, offer substantial advantages over conventional at-grade intersections and grade-separated interchanges.
The FHWA Alternative Intersection and Interchange Report (AIIR) provides information on each alternative treatment covering salient geometric design features, operational and safety issues, access management, costs, construction sequencing, environmental benefits, and applicability.(2) This TechBrief summarizes information on HCM Chapter 23, specifically with regard to the new intersection and interchange designs.
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