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Diverging diamond interchange mulled for Pleasant Hill/I-85

Photo by Nate McCullough

Photo by Nate McCullough

DULUTH -- For a way to clear congestion on two of Gwinnett's most clogged bridges, drivers may have to move to the wrong side of the road.

Community improvement districts for Gwinnett Place and Gwinnett Village are spearheading studies to create diverging diamond interchanges for Interstate 85 at Pleasant Hill Road and Jimmy Carter Boulevard.

"This is out-of-the-box thinking," said Joe Allen, the executive director of the Gwinnett Place district, where area business owners banded together to tax themselves and form a quasi-governmental entity. "This is a brand new concept for the interstates in Georgia."

In fact, the idea, which began in Europe, is new to the United States. There is only one such interchange open so far, in Springfield, Mo. Allen, who visited the site with a junket of transportation and CID officials, said the community there is very similar to the Gwinnett Place area: a suburban business district with lots of traffic issues. And, he added, the interchange is working beautifully.

Here's how it would work:

When drivers approach the Pleasant Hill bridge over I-85 from either direction, a traffic signal at each end will allow the traffic to cross onto the other side of the road. Then, people getting on the interstate will have a free-flowing left turn to get on the interstate, or at the next light, they will drive back to the right side of the road. A pedestrian walkway will be down the center.

The precision, officials said, is in the continuous flow onto the interstate without having to wait for a light. People getting off the interstate will also have continuous flow, allowing the traffic signals at each end of the bridge to have four cycles instead of six.

According to Allen, the CID has been studying the Pleasant Hill bridge since the group was formed more than five years ago. A few years ago, both business groups were calling for complete renovations of their bridges, contemplating another engineering marvel called a single-point interchange. The prospects were extremely costly -- more than $50 million each -- and with transportation funding at an all-time low, they were likely to take years.

The diverging diamond interchange, on the other hand, would cost about $3 million each, which the CIDs can handle themselves, with help from money set aside from the county sales tax for work on those bridges.

"We feel that by moving toward the DDI design which has been successfully implemented in Missouri, we can get the congestion relief benefits at a fraction of the cost," said Joel Wascher, a spokesman for the Gwinnett Village CID.

He said officials are looking at a completion date around the end of 2011, as opposed to taking a decade or so to secure the funding for a bridge replacement.

"Traffic is the No. 1 complaint we have," Allen said, adding that work to time traffic signals has caused significant improvement. "Everything comes back to the chokepoint at I-85. We've got to do something about that bridge."

According to an engineering report, the diverging diamond interchange would reduce the delay of going through the Pleasant Hill interchange by 26 percent in the morning.

Also, construction would not require taking property from nearby businesses, which was a possibility in the other design.

"This is a beautiful model of a project that is a public-private partnership that is going to have a huge impact," said Mark Williams, a local business owner that is chairman of the CID board. "It really became clear this was such a no-brainer. ... It was like discovering the new flavor of a lollipop."