Highlights of the Diverging Diamond Interchange (DDI) Informational Guide, Second Edition
The Diverging Diamond Interchange (DDI) Informational Guide, Second Edition is now available on TRB’s website. The 200-page manual is seven years in the making and the result of contributions from transportation experts from across the nation including Kimley-Horn’s Stacie Phillips, P.E., who played a key role in developing Guidance for Traffic Signals at Diverging Diamond Interchanges and Adjacent Intersections (NCHRP 3-113)—the research that led to the DDI guide. Here are some key highlights from that research.
- Many aspects of the design, such as pedestrian and bicycle paths and the location of signal equipment, need to be considered earlier than they would in a more traditional interchange.
- Both traffic signals operate with only two vehicular phases, offering a terrific opportunity for the use of low cycle lengths, which is useful for clearing traffic out of the center of the interchange regularly and for minimizing wait times for pedestrians, bicyclists, and vehicles.
- While the crossing path is not intuitive for pedestrians, with proper consideration, a DDI can be beneficial for pedestrians due to low signal cycle lengths, short crossing distances, and low vehicular speeds.
- Signal progression requires extensive fine tuning due to the short distance between crossovers; low, but variable speeds within the interchange; and extensive interplay between adjacent intersections, freeway ramps, and crossover movements.
Order your physical copy of Diverging Diamond Interchange Informational Guide, Second Edition or download the free PDF from TRB’s website.
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