A joint project of PCIDs, GDOT, SRTA, Dunwoody and DeKalb County.

The Perimeter Community Improvement Districts (PCIDs) and the Georgia Department of Transportation (GDOT) have launched a project to redesign the busy I-285 and Ashford Dunwoody Road Interchange near Perimeter Mall to improve traffic flow and safety. The new configuration is called a Diverging Diamond Interchange or DDI. This innovative design shifts the flow of traffic to the opposite side of the road to reduce points of traffic conflict and improve traffic flow and safety. The DDI is a proven, cutting-edge, low-cost design that provides immediate traffic relief. Under normal, free-flowing traffic conditions on surrounding highways, the I-285 and Ashford Dunwoody DDI can reduce traffic delays in evening rush hours up to 20 percent. The Perimeter DDI will be the first DDI in Georgia and could become a model for congested interchanges throughout the state.

DDI DDI - Looking North toward Perimeter Mall


  • The Ashford Dunwoody DDI is an interim design concept that doesn’t require rebuilding the interchange or widening the bridge.
  • Restriping, altered signal timing, improved turning conditions and one reconstructed ramp will be used to move traffic faster and reduce accidents due to fewer traffic points of conflict.
  • Pedestrian access will also improve with the installation of a sidewalk down the center of the bridge protected from traffic by concrete barriers.
  • The Ashford Dunwoody DDI design will be implemented and open to traffic within 2 years of preliminary engineering notice to proceed – much faster than any full interchange reconstruction.
  • GDOT awarded a $4.6 million construction contract in August 2011 to E.R. Snell Contractor of Snellville to reconfigure the I-285 interchange at Ashford-Dunwoody Road.
  • The PCIDs initiated the project in 2009 by making a $100,000 business investment in hiring Moreland Altobelli engineering firm to find an innovative way to improve the interchange.
  • PCIDs secured project design and engineering funding from the State Road and Tollway Authority and DeKalb County - Project received an $800,000 grant from SRTA and $450,000 from DeKalb County.
  • GDOT says this project may become a model for congested interchanges throughout Georgia.
  • Construction work began in January 2012; the project will be completed in Fall 2012.
  • The DDI design originated in France.
  • The Ashford Dunwoody DDI is the 12th DDI in the US and the first in Georgia. There are currently 11 other DDIs in four states.