The Diverging Diamond interchange (DDI) 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.

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.

Vehicles are guided safely through the interchange using signals, signs and pavement markings.

Drivers moving from south to north through the interchange will first have the opportunity to make a free right onto eastbound I-10 using the far right lane. If they continue straight, they will approach a signal at the south crossover point. When the signal is green, vehicles will cross left onto the west side of the bridge over I-10. If they are in one of two left turn lanes, they will enter the ramp to westbound I-10 without waiting for a signal. If they wish to continue north on Houghton Road, they may continue through the interchange moving back to the right side of the road at the north crossover signal. Traveling from north to south will work the same, except in reverse.
Drivers on eastbound I-10 exiting at Houghton Road will either turn right onto southbound Houghton Road, similar to a traditional interchange.  Or drivers will turn left at a signal onto the left side of Houghton Road to cross I-10. They will approach a signal at the north crossover point, and when the signal is green, they will switch to the right side of the road and continue north.

Recently IDOT constructed a DDI at I-88 and Route 59 near Chicago. This DDI’s design is similar to what is I-10 and Houghton Road.

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