The district’s board of directors approved Thursday spending $158,000 for a concept drawing of an interchange project at the intersection of Windy Hill Road and I-75. The group has had the congested interchange in mind for close to 25 years, spending about $3 million on studies and concepts.
Now, it wants to see a new kind of intersection, called a diverging diamond interchange.
The interchange would switch lanes to opposite sides of the road without stopping, alleviating the need for a left-turn signal for motorists entering the interstate. After the interchange, lanes return to their original sides of the road.
“It cuts down all those left-hand movements across incoming traffic,” said board Chairman Tad Leithead.
Early estimations, Leithead said, indicate traffic could be improved as much as 30 percent.
The entire cost is expected to be about $19 million. The CID hopes to fund that with $5 million combined with $7.5 million from the county’s transportation department and $12.5 million from state and other sources.
That’s less than what other concepts have projected. Leithead said a design for a collected distributor system, a series of roads that would run parallel to I-75 including HOV lanes would have cost $180 million to build.
Faye DiMassimo, the county’s transportation director, said the lower cost is because the design, unlike its predecessors, does not require complete reconstruction of the interstate overpass.
“I think we’ve identified the right solution at the right time,” DiMassimo said.
When polling was completed leading up to the failed TSPLOST vote last year, DiMassimo said Cobb residents ranked the Windy Hill Road interchange as their highest priority transportation project.
Commissioner Bob Ott, who represents the Cumberland area, expects the redesign to have a large impact on Windy Hill Road traffic and motorists on the interstate.
The $19 million interchange design will be done in conjunction with a separate road project widening Windy Hill Road between Cobb Parkway and Powers Ferry Road using $25 million in Special Purpose Local Option Sales Tax.
“The diverging diamond is basically the interchange between those two projects,” Ott said.
Combined with Gov. Nathan Deal’s optional toll lanes along Interstates 75 and 575 through Cobb and Cherokee counties, Ott hopes the Windy Hill Road projects will have a large long-term impact on congestion.