CDOT, City of Grand Junction Partner on State's First Diverging Diamond Interchange

July 12, 2013 - Traffic switch Monday to accommodate construction at I-70 and US 6/50.

GRAND JUNCTION—The Colorado Department of Transportation and the City of Grand Junction have partnered to bring the state its first Diverging Diamond Interchange (DDI) – an innovative interchange design that improves efficiency by eliminating some wait time for left-hand turn movements. This project represents a partnership between CDOT and the City of Grand Junction to improve safety and traffic flow on I-70 at Exit 26 (at US 6 & 50). The contractor began mobilizing equipment to the area on July 8, and traffic impacts will begin this Monday, July 15 (see Traffic Impacts, below).

The I-70 DDI is the first in the state—some 15-plus DDIs have been built in the US, the first being in Springfield, MO. The I-70 DDI project, which will continue through November 2013, 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-turn movements is twice that of a conventional diamond. Safety has been shown to increase at interchanges and intersections built as diverging diamonds. The amount of crashes is reduced, as are the severity of crashes. The accidents that do occur are at angles that eliminate the dangerous “T-bone” that can happen at a traditional signalized intersection.

The total cost of the I-70 DDI is $4 million,* whereas other alternatives for interchange reconstruction are between $10 and $15 million. Minimal right-of-way acquisition is required for this type of intersection. The work was contracted to Lawson Construction of Longmont, CO.

“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 tax-payers’ dollars.

TRAFFIC IMPACTS: Starting at 7 p.m., this Monday, July 15, motorists on US 6/US 50 will be switched to the eastbound lanes, with a single lane in both directions (the turn lanes onto the I-70 ramps will remain). The speed limit will be reduced from 45 mph down to 35 mph. This traffic switch will remain in place 24/7 until the work in the westbound lanes is completed—likely early September. Then, all traffic will be switched onto the newly configured westbound lanes. The project is scheduled for completion in late 2013.

The City also has an adjacent project underway at 22 Road (see below); CDOT and the City are working together on the timing of these two projects at 22 Road and at the I-70 DDI to minimize impacts to travel through this area.

CITY PROJECT - City of Grand Junction – 22 Road Improvements, March 2013 through August 2013: The City is realigning the 22 Road and US 6 intersection, moving it 500 feet west. This lengthens the intersection spacing with the I-70 interchange ramps, which will improve traffic efficiency and safety. A new connecting street will link Valley Court to 22 Road. Traffic will be able to access US 6 via the signalized intersection at 22 Road, eliminating the need for left turns out of Valley Court and improving safety.

PROJECT INFORMATION - Additional information on these two projects is available via the following:

*CDOT’s DDI will be paid for, in part, with FASTER funds. Funding Advancements for Surface Treatment and Economic Recovery was established by the Colorado General assembly via Senate Bill 09-108 ( to fund the repair or replacement of Colorado’s poor-rated bridges and make safety improvements to Colorado’s key corridors.