The Colorado Dept. of Transportation and the city of Grand Junction are partnering to bring the state its first diverging diamond interchange. The DDI is an innovative interchange design that improves efficiency by eliminating some of the wait time for left-hand turns.

Map courtesy of CDOT

A DDI eliminates traditional left-hand turns by crossing lanes and shifting drivers to the left side of the road. This gives drivers direct access to a left-hand ramp to access the interstate without waiting at a traffic signal.

The project represents a partnership between CDOT and the city of Grand Junction to improve safety and traffic flow on I-70 at Exit 26 (U.S. 6 & 50). The contractor began mobilizing equipment to the area on July 8. The I-70 DDI is the first in the state—some 15-plus DDIs have been built in the U.S., the first being in Springfield, Mo. The I-70 DDI project, which will continue through November, was designed by the city of Grand Junction and is being constructed by CDOT.

A DDI eliminates traditional left-hand turns by crossing lanes and shifting drivers to the left side of the road. This gives drivers direct access to a left-hand ramp to access the interstate without waiting at a traffic signal. The lanes then shift drivers back to the right side.

Diverging diamond interchanges can carry much more traffic than conventional diamond interchanges, and the capacity for left turns is twice that of a conventional diamond.

Safety has been shown to increase at interchanges and intersections built as diverging diamonds. The number of crashes is reduced, as are their severity. Accidents that do occur are at angles that eliminate the dangerous “T-bone” crashes that can happen at a traditional signalized intersection.

The cost of the I-70 DDI is $4 million, whereas other alternatives for interchange reconstruction are between $10 million and $15 million. Minimal right-of-way acquisition is required for this type of intersection.

“This is a first-of-a-kind project for us, and we are very excited to implement this DDI in an area where traffic and commerce are growing rapidly,” CDOT Chief Engineer Tim Harris said. “This project represents a successful public-public partnership, and one that capitalizes on efficient and effective use of taxpayer dollars.”