SR 115 (US 129) Alcoa Highway Relocation and Reconstruction, Hall Road (SR 35) to Little River

Tennessee’s Alcoa Highway, also known as SR 115 or US 129, is a crucial north-south, four-lane arterial connecting the communities of Maryville and Alcoa as well as the McGhee Tyson Airport to the City of Knoxville. While the Alcoa Highway is the primary commuting route taken to and from Knoxville, it also provides access to Tennessee’s freeway system. As the area develops, traffic demand will rise, creating the need for additional capacity. Currently, the existing average annual daily traffic is 51,070 and is projected to reach above 70,000 by 2037. The Tennessee Department of Highway (TDOT) hired Lochner to design the relocation and reconstruction of a particularly congested portion of the Alcoa Highway. The roughly seven-mile-long project area spans from Hall Road (SR 35) to the Little River.

Constrained by a restrictive right of way, sixteen alternatives for the relocated corridor were studied during the environmental phase. Lochner used industry leading tools to identify the pros and cons of each alternative and generated 3D models to fully understand the impacts of each alternative and the cost associated with construction.

The urban-style corridor and its seven interchanges were developed by studying traffic. Synchro and HCS7, highway capacity software, were used to understand the complex roadway segments. Each alternative underwent scrutiny and was optimized to provide efficient travel for motorists. Turning movements, weaving segments, lane capacity, and safety were all considered when selecting a preferred alternative. In addition to the sixteen corridor alternatives, seven additional alternatives for the interchange with the Pellissippi Parkway were also studied, including an innovative turbine type interchange. The new design for the Pellissippi interchange features a collector distributor with a fly-over ramp arrangement to provide system-to-system connectivity within a minimal footprint.

Design for the project has been broken into four segments. All four segments were designed to meet freeway standards with limited access at 60 mph and to accommodate four lanes of through traffic with the potential to widen into the median. While the first three design segments relocated the Alcoa Highway to the south of its existing location, the fourth segment—known as the Little River segment—reconstructed the highway in its existing footprint. This segment was particularly challenging as the corridor is lined with existing businesses that create a highly constrained right of way. Additionally, traffic in this segment needs to be maintained during construction as the corridor provides vital access. To address the space constraints and access needs, the Lochner team drew on its national expertise to incorporate a solution used previously in Texas. The design repurposes the existing roadway to be a one-way frontage road couplet system, connecting beneath the Alcoa Highway via roundabouts. The frontage roads are intended for local traffic while the freeway-style Alcoa Highway accommodates commuter-through traffic. This innovative design maintains critical access while the fourth segment of Alcoa Highway is constructed and, once complete, provides motorists with a corridor that effectively fits within its context and offers a continuous traffic flow for its varied users.

Stakeholder coordination with local residents and businesses, McGhee Tyson Airport, the City of Alcoa, and the Alcoa Aluminum Plant played a crucial role during design, allowing for the optimization of the proposed system to meet the needs of all users. As a result, Lochner created a feasible constructability plan as part of the design, which allows for all existing lanes of traffic to be open during the construction period. These open lanes will be especially crucial for the first segment of design near the Tyson McGhee Airport where two new bridges must be built near the existing corridor.

Additional Lochner responsibilities include the development of visualizations for all projects along Alcoa Highway, including those outside Lochner’s four design segments. The purpose of these visualizations is to illustrate complex design plans for the public. They have also played an important role in the right of way process, helping appraisers to understand proposed designs before beginning the acquisition process.