What’s a Diverging Diamond?

Approximately a week ago I was notified by the Governor’s Office that the Perimeter Community Improvement District (CID) will be receiving a grant of $800,000 and a loan of $684,000 from the state infrastructure bank to construct a “diverging diamond” interchange at the junction of Ashford Dunwoody Road and I-285. The project will span as far south as the Ashford Green building and as far north as Perimeter Mall.

This begged the question: What is a diverging diamond interchange?

The answer: It’s an unusual interchange design where the traffic on the non-highway road (Ashford Dunwoody) drives on the opposite side of the road (the left-hand side) as it passes over the highway. It appears that this design will greatly improve traffic flow over I-285 and will be a remarkable improvement over the current layout.

Dunwoody City Councilman John Heneghan has posted more information on his blog, and there is a good article about the redesign in the Dunwoody Crier (click for links). You can find diagrams of the new layout in both places.

Construction is anticipated to begin in 2011.

2 Responses to What’s a Diverging Diamond?

  1. [...] Diamond in Motion A couple of months ago, I reported to you (click for article) that the Perimeter Community Improvement District (PCID) is receiving a grant [...]

  2. [...] UPDATE!  Apparently there are also DDIs under construction at Ashford-Dunwoody and I-285 and someplace called “Cobb County.” More “how they work” details on that project are available at John Heneghan’s Dunwoody blog and “where the money comes from” details at State Rep. Mike Jacobs’ blog. [...]


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