TDOT awaits green light from feds to reshape I-40 exit 407 into a diverging diamond interchange

1:13 AM, Jan 24, 2012   |    comments
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TDOT is waiting for the green light from the Federal Highway Administration (FWHA) to build a gem of a design at one of East Tennessee's busiest intersections.

"If you've been at the 407 exit [on I-40], then you have sat in traffic before," said Steve Borden, TDOT Region 1 Director.  "There at the interchange of I-40 and Highway 66 you routinely have traffic that backs up off the ramp and into the right lane of the interstate."

TDOT has submitted a proposal to the FHWA to reshape the junction into a diverging diamond interchange.  The first diverging diamond design was first implemented in the United States in 2009.  TDOT constructed a diverging diamond in Alcoa at the interchange of Middlesettlements Road, Bessemer Street, and U.S 129.

Borden said a diverging diamond at exit 407 could free up traffic flow for millions of drivers who use Highway 66 as the gateway to the Great Smoky Mountains National Park.  The main change involves weaving traffic to flow in the opposite direction on each of the two Highway 66 bridges that overpass I-40.

"A diverging diamond is a new technology with interchanges. Even as an engineer you look at it and say, 'Oh gosh, I'm driving on the wrong side of the road.'  But when you actually drive it, it is very natural and you don't notice it," said Borden.

This diamond shape means drivers never have to wait and yield to head-on traffic to make a turn.  North Carolina's DOT has posted a visualization on YouTube of how a diverging diamond interchange flows.

"It allows us to get large volumes of left turn traffic without any conflicts.  It is almost like going up a one-way street and turning left where you don't have a conflict," said Borden.  "The diverging diamond is very efficient and it speeds things up.  Our studies show it will cut the length of time it takes to get through the intersection by more than two and a half minutes.  It also increases the average speed of the traffic flow by 12 miles per hour."

The compact design of the diverging diamond interchange means the state can build the project on a fast track. 

"We're able to fit within that existing right of way footprint.  That makes things go a lot faster when you don't have to buy new land and do environmental impact studies.  It also saves lots of tax dollars because we're talking about this being between $10 million and $12 million. The other alternatives we looked at would be $25 million and $30 million," said Borden.

TDOT expects the FWHA to approve or reject the proposal later this spring.  The project also needs funding from the state.  The City of Sevierville has already pledged $1 million towards the construction of the interchange.

"It's exciting when you've had an issue or a problem on your infrastructure or roadway and now we have something that looks like a really good fix," said Borden.

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