Nearer the starting line
Rework of I-75/I-24 split could begin as soon as 2019
It’s going to be a big deal. Drawings for the proposed improvements at the Interstate 75-Interstate 24 “split” show dramatic changes in store for the notorious interchange where daily backups snarl traffic, cause crashes and force drivers into last-second jockeying for position as if they’re going into the first turn at Daytona.
The split, near the TennesseeGeorgia line, sees many crashes and semitractor-trailer rollovers, with speed often being a contributing factor, according to a 2006 report.
“Rear-end and sideswipe crashes were found to be high on I-75 northbound, which are due to short merging distances between the Ringgold Road interchange and the I-24 interchange,” the report by Palmer Engineering states. “The on- and off-ramps at the welcome center located between the Ringgold Road and I-24 interchanges also contribute to these crashes.”
And the report predicted traffic problems with the existing design would only increase.
In 2017, Tennessee Department of Transportation Commissioner John Schroer called the I-75/I-24 split “about the worst interchange in the state of Tennessee.”
State officials said work at the split likely won’t start until the summer of 2019, TDOT spokeswoman Jennifer Flynn said.
The project cost is estimated at $65 million, according to the IMPROVE Act list signed into law in April 2017 by Gov. Bill Haslam. A final cost won’t be known until the final design work is done. The act and some one-time funding increases combined to move several key transportation projects forward, including others in Blount, Knox, Davidson and Shelby counties.
To streamline the project, the state is using a new approach called “design-build,” a project delivery method that combines in a single contract all or some parts of the design and construction phases, including design, right-of-way acquisition, regulatory permit approvals, utility relocation and construction. However, the project is a little behind the original schedule, which planned for the work to start by fall, officials said.
Mississippi-based NeelSchaffer Inc. was awarded the contract Jan. 5 to provide engineering services as the state’s representative on the project leading to the next step in the process. Neel-Schaffer’s role will be developing a plan for the project that gives basic design information on how the state thinks the project should be built, Flynn said.
A “design-build” contractor will be selected after a request for proposals is issued later this summer, she said. That contractor will take Neel-Schaffer’s plan and refine it to define the cost and function. Flynn said there could be alternative design concepts at that point that improve function, reduce costs and speed up the construction. A finalized plan for the project will be the result of that process.
According to the current proposed plan, most of the existing interchange roadways will be moved and straightened as part of the improvements. The design incorporates less dramatic curves and bridges called “flyways” that allow more room for the interchange ramps to pass
under and over each other. The interchange at I-75 and Highway 153 is a scaled-down example of the design.
To understand how the current proposed design will look, it helps to think of it from a rushhour perspective.
INBOUND PROPOSAL
Southbound I-75 traffic will see the first improvements in the form of a lane added on the right side just after the East Brainerd Road interchange to make a fifth lane going into the split, according to plan documents. That’s where the center lane will fork with the three right lanes becoming I-24 West (rather than two) and the three left lanes heading south on I-75.
Northbound I-75 traffic from Georgia won’t see any changes until after passing under the Ringgold Road overpass at East Ridge. But where northbound
traffic can take exit 1, the exit lane there will become a lane that continues north and is joined by another lane to its right that will allow traffic to hit an exit ramp for the Tennessee welcome center.
That’s where it gets interesting, because the welcome center and exit 1 ramps create some complications.
With five lanes heading north into the split, the center lane will fork, the three right lanes will become a ramp onto I-24 West — exiting to the right instead of the current two-lanes-mergedinto-one nightmare that exits to the left for I-24 and causes much of the northbound backup — and the three left lanes will continue as I-75 North with a gentler curve to the right.
Welcome center and northbound exit 1 traffic will have a new, shared ramp that passes behind the welcome center
facility where drivers will have a choice at a fork to go north on I-75 or west on I-24. There will be no more mad dashes across all the lanes to get over to I-24.
OUTBOUND PROPOSAL
Drivers on I-24 headed east out of downtown Chattanooga will start seeing changes between the Belvoir Road and Moore Road bridges, according to documents. There, a fourth lane will begin with the South Terrace to I-24 East on-ramp between Belvoir and Moore and will continue to be joined by a fifth lane formed by the next on-ramp after the Moore Road bridge.
As those five lanes reach the split, the center lane will fork with the three left lanes continuing to I-75 North and the three right lanes continuing onto I-75 South. At that point, the three southbound I-75 lanes and the three merging I-24 lanes will combine briefly as the two right lanes become the off-ramps for exit 1 at East Ridge. Southbound I-75 will return to three lanes by the time it reaches the Georgia state line.
RELATED WORK
The bridges over I-24 at Moore, McBrien and Spring Creek roads will be replaced to allow the added lanes to pass under them. Where I-24 East merges onto I-75 South, the curve no longer will be so sharp and unused ramps and lanes will be removed, according to documents. Also, other project area bridges over creeks and a railway could be modified or replaced as part of the work.
Flynn said the impact on adjacent properties along the project corridor won’t be known until the design-build contractor is selected, and the split project will have no effect on the ongoing work at exit 1.
“That project was designed with the future I-75/I-24 interchange project in mind,” Flynn said.
Neel-Schaffer provided design work on road improvements related to the replacement project for the lock at Chickamauga Dam. The firm was selected for the project by the U.S. Army Corps of Engineers. The $6 million project included two bridges, two roundabouts, retaining walls and about a halfmile of roadway, according to project information on the company’s website.