Abstract
A diverging diamond interchange (DDI) is an innovative interchange design that is being used with increasing frequency in the United States because of the ability to use existing right-of-way and infrastructure frequently. This paper documents the state of the practice in DDI signal phasing with principles established in the Signal Timing Manual, namely, that it uses consistent phase numbering in a logical format to describe each of the phasing concepts being considered and discussed in this paper. Although some literature exists on several methods of signal phasing for DDIs, inconsistency in the reporting leaves practitioners scratching their heads when attempting to decipher what phasing scheme to use. In response, three fundamental phasing schemes are presented, one each for volume patterns with two, three, and four critical movements. Each scheme is described with a consistent naming convention, and, when possible, each is manipulated to provide varying coordination strategies. In addition, concepts such as use of actuation and barriers to improve coordination are described, and methods for reducing lost time are introduced. Other supplemental information related to preemption and pedestrians is discussed briefly. In conclusion, practitioners are given some basic guidance on when one phasing scheme may be more appropriate than another.
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