INNOVATIVE INTERCHANGES

Diverging Diamond Interchange (DDI)

What are innovative interchanges? Interchange designs where traffic movements are modified to improve safety, reduce delay, and increase efficiency.

Visit www.virginiadot.org/innovativeintersections to learn more.

I-64 at US 15 (James Madison Hwy), Zion Crossroads, VA

A DDI IS ALSO KNOWN AS:

� Double Crossover Diamond Interchange

What is a DDI? � A grade-separated interchange design where arterial traffic crosses to the other side of the roadway between the freeway ramps

� Vehicles can turn left onto and off freeway ramps without stopping or crossing opposing lanes of traffic

� Right turns onto and off the freeway ramps occur either before or after the crossover intersections, when traffic is on the “correct” side of the road

� Both crossover intersections are signalized

� Interchange can be designed as an overpass or underpass

When should a DDI be considered?

� At locations with heavy left-turn traffic volumes onto and off the freeway ramps

� At locations without adjacent traffic signals or nearby driveways

� At locations where there is limited roadway width for left-turn lanes between ramp intersections and limited right-of-way to expand

What are the benefits of a DDI?

� Improved safety: Reduces the number of points where vehicles may cross paths

� Increased efficiency: Crossovers can operate with only two traffic signal phases, which allows the interchange to handle a greater volume of traffic and operate with less delay

� Easier access to freeway: Design allows traffic to enter and exit the freeway without crossing opposing lanes of traffic

� Cost effective: Since there are no left-turn lanes on the arterial, a DDI can have a narrower cross section and may be more cost effective than a retrofit or new interchange construction

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