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A COMPARISON OF TWO DIAMOND INTERCHANGE FORMS IN URBAN AREAS

Diamond interchanges, because of their minimal right-of-way requirements have become desirable in highly developed urban areas. Many existing conventional diamonds are currently being converted to single-point and compressed diamonds. These have different operational/capacity characteristics and construction costs. The article attempts to clarify some misunderstandings and provide direction as to the application of these two diamond forms in urban areas. The intersection geometrics for the two forms are discussed, and two designs, one for each interchange are presented. Operational characteristics relating to signalization/phasing requirements, clearance time, saturation flow rates for various through and turning movements, and safety are discussed. Bridge design, right-of-way, future flexibility, and construction costs are covered. The determination of the relative efficiency, capacity, and level of service of single-point and compressed diamond interchanges are discussed. The existence of frontage road conditions are also discussed. The study found that applications are limited for the single-point diamond. The compressed is less costly, has similar right-of-way requirements, and is more efficient.