Preliminary Environmental and Engineering Work Set Stage for Major Corridor Redevelopment

Located in the heart of South Carolina, the I-20/26/126 corridor is the crossroads of the state economy and the major hub for the Midlands’ commuters, travelers and commerce. In addition to being a main route in and out of Columbia, I-26 is a thoroughfare for travelers headed to the coast and mountains and a major cargo route between Lowcountry ports and Upstate manufacturers. Last improved in the 1980s, the I-20/26/126 corridor does not meet current traffic demands and had earned the nickname “Malfunction Junction.” Finding a solution has become the state’s top interstate priority.

Since 2015, HDR has served as the prime consultant to complete alternatives development, environmental analysis and documentation, public stakeholder engagement, and preliminary design for completion of the environmental impact statement, and record of decision in spring of 2019. Following the National Environmental Policy Act stage, HDR has continued to support overall program delivery strategy, management, and implementation to deliver these much-needed and critical infrastructure improvements for the state of South Carolina.

A Multi-Phased Approach

The $2.5 billion project has been divided into multiple construction phases, with our team providing services on each phase while also supporting SCDOT with overall program management. To date, HDR has provided utility coordination, procurement development and design review support for the Phase 1 and Phase 2 design-build projects and has continued final design and plan development activities for the Phase 4 and 5 design-bid-build projects scheduled for construction in early 2027. 

When SCDOT decided to restructure its approach to the remaining project area (previously identified as Phase 3) in October 2023, HDR was charged with the task of identifying the most effective means of re-phasing the project with the least impacts to cost, schedule, or traveling public, while also addressing significant risks associated with critical utility relocations and geotechnical conditions. Our team developed and evaluated multiple re-phasing alternatives through active coordination with SCDOT to arrive at a preferred alternative and SCDOT-approved phasing plan in February 2024. Ultimately, the approved phasing plan restructures the delivery of the previous Phase 3 area into multiple, smaller phases of construction utilizing a proposed combination of design-build and design-bid-build delivery methods.

Implementation of the re-phasing plan anticipates HDR’s continued program management and strategic communications support, with additional services to include traffic analysis, final design (roadway, hydraulics, bridge, and geotechnical), design-build procurement development, and utility coordination, as applicable to each individual phase.

Upon completion, the corridor will have added capacity with additional lanes in each direction on I-20, I-26, and I-126 as well as 12-foot inside shoulders for emergency vehicles. Traffic flow and speed will be improved through seven reconstructed interchanges, including the replacement of cloverleaf loops with smoothly flowing directional ramps and longer, separated exits. When the project is complete, these changes will save each driver an average of 112 hours per year that would have otherwise been spent sitting in traffic.

New Approach for Design-Build Permits

Knowing changes to the design may happen during the construction phases, our team coordinated with SCDOT and the USACE to determine that a more flexible approach was needed for such a large, multi-phase design-build project. This innovative approach estimated the overall impacts and allowed permit modifications to be made within applicable design-build contracts and as final design is developed for design-bid-build phases.   

The permit also included permittee responsible mitigation which provides 65,000 linear feet of stream restoration and preservation and wetland mitigation to make up for the impacts associated with construction of the project. The plan will be maintained by the South Carolina Department of Natural Resources when the project is completed.

The first two phases of the project are currently under construction and scheduled for completion in 2024 and 2025, respectively, with the entire project anticipated to be complete in 2034.