Located in southeastern Tennessee, downtown Chattanooga is just 5 miles from the Georgia border. One of the main routes that drivers take between the two states, Interstate 75 (I-75), traverses the entire state of Tennessee and runs from Florida to Michigan. The route comes together at Interstate 24 (I-24), which runs from Chattanooga to Illinois. At the I-75/I-24 interchange, the Tennessee Department of Transportation (TDOT) and general contractor Wright Brothers are nearing completion on a project that will offer drivers multiple benefits.
Since it was constructed in the early 1960s, the interchange has been widened. While the widening helped with capacity, the average daily traffic (ADT) in the area continues to grow. In 2023, the ADT on the interchange was 137,000, and it is expected to reach 155,000 in 2043.
The project is needed to improve the interchange operations, including safety, and make it more reliable. According to Daniel Oliver, Assistant Chief Engineer of Region Two, where the project is occurring, a primary safety issue is caused by the weaving that occurs as drivers enter the interchange.
The current I-75/I-24 interchange modification project is phase two, with the first phase being completed in 2021.
“There are multiple factors behind dividing the project into two phases,” said Rae Anne Bradley, Regional Communications Officer for TDOT. “However, the primary reason was funding, as Tennessee is a pay-as-you-go state.”
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The scope of the first project included widening each leg of the interchange, constructing a new on-ramp to provide access to both I-75 and I-24, 11 new bridges, and two I-24 overpasses along Spring Creek Road.
“We split the project into two phases to minimize temporary construction as much as possible,” Oliver said. “We didn't want to build something that had to be torn out later.”
The current project has three segments. The first is on I-24, the second is on I-75, and the third, according to the project page on TDOT’s website, is on interstate-to-interstate ramps within the I-75 and I-24 interchange. The website said that “ramps previously reconstructed during Phase I of the project will be resurfaced and restriped to create additional travel lanes. Overhead signs will be adjusted to match the new interchange layout.”
The primary element of the project is to add one lane in every direction. This includes adding a lane to all interchange ramps, a 1-mile-long lane on I-75 in each direction, and a 1.5-mile lane on I-24 in each direction.
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Other work on I-75 includes:
- Improving the southbound entrance ramp to eliminate a merge
- Replacing median barriers, guardrails, signing, and lighting
- Rehabilitating existing concrete pavement
- Replacing the I-75 bridge over the CSX railroad
The additional work on I-24 includes:
- Widening a westbound exit ramp
- Replacing the concrete pavement with asphalt
- Replacing the storm drainage system, median barriers, guardrail, signing, and lighting constructing
- Installing new retaining walls and noise barriers
- Replacing two overpass bridges
- Modifying entrance and exit ramps to eliminate a traffic weave and lengthen merge lanes
- Owner: Tennessee Department of Transportation; William Curtis, Project Manager
- General Contractor: Wright Brothers, Charleston, Tennessee; Brian Charlesworth, Project Manager
- Project Designer: RK&K, Baltimore, Maryland
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Because the interstate is so widely used, the team needed to minimize disruption as much as possible. The contract stipulates that three lanes must remain open throughout the project.
“We implemented a lane rental program where the contractor can reduce open lanes for three straight days,” said William Curtis, a Project Manager for TDOT. The contractor can do this two times throughout construction. The first time they did a lane rental, the work only took two days.
The construction and design teams meet weekly. One of the agenda items is to plan out the next six weeks of construction. Impacts to traffic are planned well in advance to allow TDOT to analyze the temporary lane closure and provide advanced notice to motorists.
“During a recent meeting, the contractor submitted a request to utilize a lane rental,” Oliver said. “We reviewed the request to see how it will impact traffic regionally and if significant events are coming up.”
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The traffic control on I-24 was approached in two phases. In phase 1, traffic was pushed to the center while crews worked on outside improvements. In the second phase, traffic was pushed to the outside while crews focused the work in the center. A temporary barrier was used to separate the work zone from traffic to ensure the safety of the crews and drivers.
The project involves replacing parallel bridges that cross I-24. Initially, the plan was to replace one bridge at a time. However, the design-build team reconsidered the decision and realized traffic could use side roads as a giant U-turn.
“We turned this into an opportunity because removing the bridges simultaneously saves time for the project,” Oliver said.
The CSX railroad bridge under I-75 presents another challenge. The railroad adds another stakeholder to the mix. The team must work through their review processes. They had to handle dirt around the railroad and reinforce existing slopes. Working around the railroad requires flexibility, as there are live trains. When the railroad gives the team windows of opportunity to work, they need to react quickly.
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Another twist is that the property owner under the bridge is the state of Georgia. However, they are not involved with the project.
The team is replacing the pavement on I-24 as part of the contract. The surface is all concrete, but the replacement will be full-depth asphalt. Wright Brothers uses a multi-head breaker rubblizer with a high-impact hammer to remove the concrete. The old concrete is used as the new surface’s aggregate base.
Rubblizing minimizes demolition. Reusing the concrete means it does not have to be trucked out, and new material does not have to be produced and brought in. Therefore, the process saves time and money and reduces the carbon footprint.
This project is being delivered via the design-build delivery mechanism. Oliver said that the state has been using this delivery method more frequently recently and that the project type drove their decision to utilize design-build.
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“Complexity and time also drive the decision,” TDOT Regional Director of Operations Adam Casteel added. “This is a significant project based on the impact of traffic. We can get the project completed more quickly while minimizing impact.”
“The sooner we can let the project, the cheaper it will be,” Oliver said. He expects the state to use the design-build delivery method more often. "As we get more comfortable with it and our partners gain more experience operating this way, I expect us to use it more often when and where appropriate."
RK&K, headquartered in Baltimore, Maryland, is the design lead, while Wright Brothers Construction Company, Inc., based in Charleston, Tennessee, is the general contractor. TDOT selected the team based on the fee and project duration.
TDOT has worked with Wright Brothers before. Oliver noted that the firm has experience in alternative delivery methods.
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“They communicate well internally and externally and quickly react to issues as they arise,” he said. “Wright Brothers manages their forces well to be keep the work on schedule.”
Construction began in spring 2023, and the anticipated completion date is late summer 2025. The project is currently on schedule.
The design-build method has helped progress the project. Another element that benefited the project was that very little right of way needed to be acquired.
The construction budget for the project is $161 million. The federal and state governments are funding the project via a 90/10 split, respectively.
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When the second and final project related to the I-75/I-24 interchange is completed, drivers will experience increased safety and predictability. The project will also remove deficiencies in the existing interchange and provide congestion relief. Currently, there is often a bottleneck between the interstate and the state line. The noise barriers will provide relief for residents and business owners in the area. Finally, bicyclists and pedestrians alike will have new widened pedestrian facilities, along with the pair of bridges.
