Diverging Diamond Interchange (DDI)

The Diverging Diamond interchange was first proposed in the U.S. by the University of Maryland in 2000. Following an intensive study of the design by the Federal Highway Administration (FHWA), the first such intersection in the U.S. was completed in Springfield, MO in 2009. There are now over 90 DDIs across the country with many more in the design or construction phase.

How Diverging Diamonds Work

A DDI is a diamond interchange on which the two directions of traffic on the cross street (above or below the freeway) cross to the opposite side on both sides of the bridge at the freeway. In the United States, more than 90 DDIs have been constructed in 29 states since 2009. The design has increased in popularity because of safety, operational and cost benefits. DDIs can reduce the number and severity of crashes compared to traditional diamond interchanges, while reducing traffic congestion. They also provide an excellent opportunity to integrate multimodal facilities for pedestrians, cyclists and transit into the interchange. They can be more cost effective to build, and there are fewer impacts on the local community during the construction process.

If you’re curious to see how a DDI works, watch this video from the Illinois Department of Transportation (IDOT). Recently IDOT constructed a DDI at I-88 and Route 59 near Chicago. This DDI’s design is similar to what is I-17 and Happy Valley Road.

Diverging Diamond Interchange Animation (Illinois DOT) from Inside ADOT on Vimeo.