What is a Diverging Diamond Interchange (DDI)?

Aerial rendering of the future Exit 16 Diverging Diamond Interchange
Aerial rendering of the future Exit 16 Diverging Diamond Interchange. Enlarged view.

A Diverging Diamond Interchange (DDI) is an innovative, modern interchange design that can relieve traffic congestion and improve safety for drivers, bicyclists and pedestrians.

In a DDI, traffic crosses to the left side of the roadway allowing for ease of access to the interstate by eliminating difficult left turns. With traffic diverted to the left side of the roadway, vehicles making a left onto the interstate entrance ramps do not have to cross oncoming traffic, creating fewer conflict points. The reduction of conflict points eliminates potential user collisions, thus improves safety and vehicle throughput. With left turn movements operating freely within the DDI, the traffic signals no longer require protected left turn phasing, improving overall traffic operations at the interchange. Additional benefits include reducing driver discomfort, fuel consumption, and lost time. The DDI’s channelizing raised islands significantly reduce the number of wrong-way entrances onto the interstate.The raised islands also create short crossing distances, which increase overall safety for non-motorized users such as pedestrians and bicyclists.

In addition to the safety and operational benefits of the DDI, the construction of a DDI is cost effective. The DDI can be constructed utilizing the existing bridge structures eliminating the need to modify or replace them, reducing construction costs. The construction schedule of a DDI is much shorter than the construction of more common interchanges not only reducing overall cost, but also impacts to the traveling public.