Diverging Diamond Interchange

A Diverging Diamond Interchange (DDI) is a relatively new design that allows for more efficiency and higher capacity than a traditional diamond interchange. Through-traffic on the arterial is crossed from the right side to the left at the signal prior to the interchange bridge and crossed back at the signal after. This allows left turns from the exit ramps to flow freely without a protected signal phase, which in turn reduces the number of signal phases from three to two. This makes the signal operation more efficient, resulting in better operation and higher capacities. Missouri may be the first in the U.S. to implement the DDI as part of an interchange project. In 2007, a planning study in Lexington, KY recommended a DDI at one interchange location.

References

FHWA Roads & Bridges Article
A diverging diamond interchange (DDI), born in the City of Lights in the mid-1970s, is currently under construction in Kansas City at the intersection off I-435 and Front Street. When completed, it will be the first interchange of its kind in the U.S. As new approaches are explored to ease traffic congestion, innovative designs like this will become more abundant.

FHWA Roads and Bridges.pdf

DDI Sample Layouts

DDI Example Layouts.zip

FHWA DDI Performance Research
Transportation planners and traffic engineers are facing the challenge of inventing ways to mitigate congestion during peak hours. Alleviating delays and improving safety for passengers and pedestrians is the primary motive. On way of achieving this objective is to search for alternative intersection and interchange designs.

FHWA DDI Performance Research.pdf

Missouri DOT DDI Driving Video
View a simulation video of the diverging diamond interchange.

Missouri DOT DDI Driving Video

FHWA Tech Brief
In recent years, the FHWA has been advocating novel intersection designs as a way to promote intersection safety while meeting the often conflicting demands for increasing capacity, decreasing congestion, and minimizing the cost of new infrastructure. On of these novels designs is the diverging diamond interchange.
FHWA Tech Brief