New interchange design targets traffic snarls

North Buckhead Driving and DUI School

One of metro Atlanta’s busiest commuting hubs reopens Monday with a new design that promises fewer backups, so long as motorists can get used to driving on the wrong side of the road.
Georgia’s first “diverging diamond” interchange at I-285 and Ashford-Dunwoody Road could be a quick and, at $5.5 million, relatively cheap fix to the massive traffic backups that plague the area each day.
“I’m sure we will get used to driving on the left side of the road without having to move our steering wheel to the right side of the car,” Dunwoody resident Norbert Leahy said. “I just don’t know how we will get back to the right side of the road just yet.”
Dennis Kemp, the general manager of nearby Perimeter Mall, said he’s convinced the new design will alleviate daily backups that can leave motorists waiting more than half an hour to get onto I-285. Officials in Gwinnett County are expecting similar success with diverging diamond interchanges, or DDIs, planned for the I-85 interchanges at Jimmy Carter Boulevard and Pleasant Hill Road.
The Central Perimeter Market, which includes the Ashford-Dunwoody interchange, is the Atlanta area’s largest office market. Of the 123,515 jobs in the area, 88 percent are filled by people who commute there. And of the 65,639 people who live there, 79 percent commute to jobs elsewhere. That means some 55,000 motorists pass through the interchange daily.
The redesign will channel traffic on Ashford-Dunwoody Road into the two left lanes on the overpass so those wishing to turn left onto the Perimeter do not have to wait for a signal.
The lane shift may present motorists with what one traffic engineer called an initial “freak-out factor,” but it will subside with time.
Officials involved with the Perimeter project want to guard against confusion.
The Perimeter Community Improvement Districts, which initiated the project three years ago, held a dry run two weeks ago when drivers negotiated a replica of the interchange in the Perimeter Mall parking lot. Presentations, leaflets and videos explaining the design have also been circulated throughout the area.
Yvonne Williams, the president and chief executive officer of the Perimeter CIDs, said any hope of improving the intersection through normal means would have been far in the future. That plan, according to GDOT, calls for a complete reconfiguration of the bridge at an estimated cost of $170 million, including construction and right of way. Such work could not be scheduled until at least 2030.
The Perimeter CIDs initiated the DDI project in 2009 when they spent $100,000 to hire an engineering firm to find an interim solution to backups at the interchange. The PCIDs secured funding for project design and engineering from the State Road and Tollway Authority and DeKalb County. That projected cost to date totals $824,423. GDOT is funding the $4.6 million cost of the DDI construction.
That same year, Missouri built the first diverging diamond, and it has proved to be a big hit, said Don Saiko, a project manager for the Missouri Department of Transportation.
After the first interchange opened in Springfield, four more were quickly added. An additional half dozen are either under construction or in the planning stages.
Saiko said backups at the Springfield interchange on I-44 would sometimes reach three miles. Now, he said, there are no backups.
The result has turned around public opinion.
“We had comments like ‘You guys are crazy’; some were pretty nasty,” Saiko said. “Now I get calls from people saying they were wrong and we ought to put these things in more places.”
Similar results in Dunwoody could diminish Perimeter Center’s reputation for traffic jams.
Just by eliminating left-turn congestion, the project should cut light changes by one-quarter, Dunwoody Mayor Mike Davis said. As a result, he expects a 25 percent improvement in traffic flow.
“The reputation we have of traffic jams is a problem,” he said. “We can either spend tens of millions of dollars putting in a cloverleaf there and buying some of the most expensive property in Dunwoody or spend $5.5 million and try to solve it the best we can.”
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