South Carolina’s interstates receives major upgrade.
By Aurielle Weiss
Interstate 385 is a 42 mile long route connecting northwest from I-26 to the city of Greenville in the South Carolina Upstate. It serves as a commuter route for the south Greenville County suburbs while also joining the Greenville metropolitan area with Columbia.
The interchange of Interstates 85 and 385 in Greenville County is a vital link of the Interstate 85 corridor between Atlanta and Charlotte and facilitates the movement of a large number of people and goods in and through the Upstate of South Carolina.
By replacing bridges and widening the interstate, SCDOT will reduce congestion, improve safety, and ensure this vital piece of the region’s transportation system meets the needs of tomorrow’s traveling public.
The interstate has an average Annual Daily Traffic count of 200,000 vehicles. With such high numbers, it is ranked second on the SCDOT’s priority list of deficient interchanges and was imperative to improve, not only for motorists, but for businesses that heavily rely on this route for transportation.
The interchange is the first of its kind in South Carolina with all fully-directional system-to-system ramp movements, a collector-distributor system that improves traffic operations and eliminates all weaving associated with loop ramps.
A total of 13 new bridge structures were constructed including mainline interstate bridges, collector-distributor bridges, ramp bridges and the Roper Mountain Road overpass over I-85. Substructure modifications were also constructed at the Woodruff Road overpass bridge.
Operational improvements such as eliminating the tight loop ramps and replacing them with flyovers will provide free flowing directional movement through the interchange. It will also have collector-distributor lanes improving flow for through traffic and separate traffic entering and exiting the interstate.
The project was funded by multiple sources including the Federal Highway Administration, SC State Infrastructure Bank, the local Metropolitan Planning Organization and one-time state funding (Act 98). Because of the statewide impact and significance of the project, support for the project was widespread.
The Gateway Project is the first of three major projects intended to address “pinch points” in the statewide transportation system hindering the flow of goods and services. The two remaining pinch points are in Columbia and Charleston and both feature system-system interchanges that will be addressed along with other service interchanges and interstate widening.
The I-85/385 Gateway Project was the second largest in the history of the South Carolina Department of Transportation coming in at approximately $231 million.
The project was constructed utilizing the design-build process, allowing its design, environmental permitting, right-of-way acquisition, utility relocation and construction to take place under one contract.
This method helped reduce overall construction time assisting the SCDOT manage costs and encouraging the Contractor to be innovative; saving taxpayer’s money, lessening environmental impacts and shortening travel delays for motorists.
As part of the design of the project, an Environmental Assessment was completed as required by the National Environmental Policy Act (NEPA) and a Finding of No Significant Impact (FONSI) was issued by the Federal Highway Administration (FHWA). This environmental documentation ensures that the project minimizes to the extent possible impacts to both the human and natural environment.
The goals of this considerable project were many; improving safety for the traveling public, providing a financial boost to the local economy and increasing capacity of the interchange and adjacent interstate.
The project was needed to alleviate traffic volumes and existing configuration of the interchange that was resulting in unacceptable operating conditions and deficiencies along the various ramps.
Multiple merge and weave movements combined with the volume of traffic significantly impacted the operations of the interchange. These deficiencies created safety concerns due to congestion, undesirable movements and vehicular conflicts.
Reconstructing a heavily traveled urban interstate interchange while maintaining all traffic movements without long-term lane closures is an extreme challenge. Continuously adjusting the project’s work-zone traffic control strategies, in conjunction with constant communication with the motoring public through a project website and press releases, were key to providing safe access through the work zone.
Widening all four legs of the two interstates approaching the interchange on rolling terrain and minimizing property impacts to nearby businesses also brought challenges. Over 30 retaining walls of many different kinds available to SCDOT, such as MSE Walls, Pile & Panel Walls, Soil Nail walls and conventional concrete cantilever walls were employed to minimize the project footprint.
Constructing new collector-distributor roads in each direction was key in improving traffic operations and separating ramp movements from mainline traffic.
The Greenville area is home to a number of large domestic and international manufacturing facilities including BMW and Michelin and a growing population as a result of that business investment. SCDOT’s investment in this project ensures that businesses and the travelling public will have a modern, functional and safe facility for years to come.
I-85/385 Gateway Project
Team: Federal Highway Administration, South Carolina Department of Transportation and Flatiron-Zachry JV
Cost: $231 Million
Annual Daily Traffic count: 200,000
Aurielle Weiss is the Assistant Editor at American Infrastructure Magazine. She can be reached at firstname.lastname@example.org.