Diverging Diamond Interchange delayed to 2020

Concept photo of McDonough diverging diamond interchange
I-75 at state route 20 / exit 218 will be converted into a DDI next year. (Georgia DOT photo)

Residents will have to wait a few months longer before the much anticipated diverging diamond interchange breaks ground in McDonough. Georgia DOT has delayed the construction bid to a let date of May 2020 instead of the original September 2019 timeline.

Once built, the DDI will improve traffic flow and reduce crashes at I-75 exit 218 / state route 20. Construction is estimated to last ten to twelve months.

What is the DDI?

The diverging diamond interchange is an innovative roadway design that originated in France during the 1970s. It was first built in the United States in 2009.

The design utilizes a crossover, where vehicles travel on the left-hand side of the roadway within the interchange. As drivers approach an interstate exit, they crossover to the left-hand side at the first traffic signal within the exit. After traveling over the bridge, they cross back to the right-hand side at the second traffic signal. This allows left-hand turning vehicles to enter or exit the interstate without the need to turn in front of opposing traffic. Additional road signage, lane markings, and concrete medians help motorists navigate the interchange. Most drivers grow accustomed to the design after only a few trips through the exit.

A visualization is available from North Carolina DOT; I recommend this video for anyone wanting a visual aid to help understand the roadway design.

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