Improved Flow at Diverging Diamond Interchange

Provided by Susan Long from the Perimeter Community Improvement Districts

Motorists are finding traffic flowing smoother since a weaving issue that occurred after the opening of the Diverging Diamond Interchange at I-285 and Ashford Dunwoody Road last year has been improved recently through the Perimeter Transportation Operations Program (PTOP).

PTOP is a collaborative program between the Perimeter Community Improvement Districts (PCIDs) and the cities of Brookhaven, Dunwoody and Sandy Springs to upgrade and synchronize signals to improve traffic congestion in the Perimeter business district and adjacent main thoroughfares. The three-year $2.8 million program is funded by the Georgia Department of Transportation.

“Drivers exiting I-285 westbound and turning right onto Ashford Dunwoody Road were facing problems merging with free flowing northbound traffic that was coming through the DDI,” said PCIDs Program Manager Jennifer Harper.  “It was especially challenging for right turners who needed to access the offices at Ravinia on the right or to cross four lanes of traffic and turn left onto Hammond Drive.

“Through PTOP, we have worked with the City of Dunwoody to greatly improve the situation by reducing the amount of time that traffic signals were overlapping and maximizing the synchronization of signals through the DDI and along the Ashford Dunwoody corridor,” Harper said.

The change in the signal timing plan has virtually eliminated the weave issue with the exception of the weekday morning peak period, which was reduced 70 percent, Harper said.

“The right turn movement is the heaviest movement during the morning peak time - approximately 1,700 right turns,” Harper noted. “Complete elimination during the a.m. peak period wasn’t possible without causing more backup onto the interstate,” Harper explained. 

“The flow and safety of high traffic on I-285 is the highest priority for the interchange,” Harper said. “The timing plans at the I-285 westbound exit ramp at Ashford Dunwoody Road must ensure that the ramp doesn’t back up onto the interstate during the morning and evening rush hours causing a safety issue for the interstate system. The longer traffic is stopped on the ramp, the more traffic builds up onto the interstate.”