GDOT awards construction for McDonough DDI

Aerial photo of I-75 exit 218 / state route 20 (staff photo)
I-75 at state route 20 (staff photo)

A project first proposed in 2015 is going to construction after Georgia DOT awarded a contract on July 31 for the installation of a diverging diamond interchange at I-75 and state route 20 in McDonough. The project’s estimated completion date is April 30, 2022.

The low bid was awarded to CMES, Inc. of Norcross, GA in the amount of $5,215,335.76. The project is funded through federal transportation dollars.

Construction will require one weekend, possibly a second, where the bridge is closed. When this occurs, motorists will be able to enter or exit the interstate, but not cross over the bridge. These weekends will happen during later phases of construction and the dates will be communicated in advance when scheduled.

The McDonough location is the second installation of the innovative design in south metro Atlanta following I-285 at Camp Creek Parkway. The design was first implemented in Georgia in 2012 and fewer than ten are operational statewide. Examples include I-285 at Ashford-Dunwoody in Perimeter, I-75 at Windy Hill Road near the Braves stadium, and I-85 at Jimmy Carter Blvd in Gwinnett County.

Aerial photo of I-285 at Ashford-Dunwoody Road (Perimeter CID photo)
Ashford-Dunwoody at I-285 opened in 2012 as the first DDI in Georgia. (Perimeter CID photo)

Diverging diamonds feature a crossover design where drivers temporarily drive on the left-hand side of the roadway when crossing the bridge. This allows motorists entering or exiting the interstate to turn left without crossing in front of opposing traffic. The design improves traffic operations by an estimated 30–40% — reducing motorist delays — and reduces crash rates.

The interchange will feature additional pavement markings, road signs, and directional arrows to help guide motorists through the exit. When complete, the bridge will feature six lanes with a barrier-protected ten-foot wide center sidewalk for pedestrians and cyclists. The six lanes will include two through lanes and one left-hand turn lane in each direction.

Following the DDI project, widening state route 20 from I-75 to Phillips Drive is scheduled to let for construction in November 2021. The project will widen the road from two to four travel lanes and build a new multilane roundabout at the intersection of state route 20 and McDonough Parkway.

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