Diverging Diamond Interchange
A diverging diamond interchange (DDI), also called a double crossover diamond interchange (DCD), is a type of diamond interchange in which the two directions of traffic on the non-freeway road cross to the opposite side on both sides of the bridge at the freeway. It is unusual in that it requires traffic on the freeway overpass (or underpass) to briefly drive on the opposite side of the road from what is customary for the jurisdiction. The diverging diamond interchange was listed by Popular Science magazine as one of the best innovations in 2009 (engineering category) in "Best of What's New 2009".
Like the continuous flow intersection, the diverging diamond interchange allows for two-phase operation at all signalized intersections within the interchange. This is a significant improvement in safety, since no left turns must clear opposing traffic and all movements are discrete, with most controlled by traffic signals. Additionally, the design can improve the efficiency of an interchange, as the lost time for various phases in the cycle can be redistributed as green time; there are only two clearance intervals (the time for traffic signals to change from green to yellow to red) instead of the six or more found in other interchange designs. Some of the intersections in the design can be unsignalized. The left turn from the freeway off-ramp, for example, can form an auxiliary lane that then becomes an exit-only lane for the entrance ramp to the freeway in the opposite direction. Omitting the traffic signals for the left turn movements off the freeway only works well with single left turns and when short queues exist within the interchange on the arterial street.
Read more about Diverging Diamond Interchange: History, Advantages, Disadvantages, Further Considerations, Similar Interchanges
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