Alternatives Review Process

Main Road Alternatives Review Process

The Main Road Corridor project is funded solely through Charleston County’s 2016 Transportation Sales Tax. This project will require federal permits before entering construction, and therefore needs to complete the Project Development and Permitting Process. This process identifies the potential impacts this project could have on the area’s human and natural environment and narrows down a preferred construction alternative. The U.S. Army Corps of Engineers (USACE) will act as the lead permitting agency, and ultimately approve the final alternative based on the Project Development and Permitting Process. 

Alternatives Review

Seven conceptual alternatives for the interchange at US 17 and Main Road and three conceptual alternatives for the River Road/Chisolm Road intersection have been developed.

Main and US 17 Interchange Alternatives

Based on the primary purpose, the project team evaluated the predicted level of service (LOS) for each of the preliminary alternatives based on current traffic volumes. LOS is a standard measurement based on vehicle speed and delay and is represented by a letter A, B, C, D, E, or F. LOS A represents free flow traffic conditions, progressing incrementally worse through each letter to LOS F which represents unstable traffic flow. Three preliminary alternatives showed a LOS of D and were eliminated.

A second screening was completed to evaluate an environmental review based on already available information. These were: National Wetland Inventory mapping, estimated right-of-way impacts and relocations, floodplains, cultural resources (known and potentially eligible historic sites), and farmlands.

River Road/Chisolm Road Alternatives

Three alternatives for the River Road/Chisolm Road Intersection were generated and evaluated. Based on the first and second screening, no alternatives were eliminated and all three will be carried forward as reasonable alternatives.

Mainline Main Road and US 17 Alternatives

The intersection improvements at US 17 and River Road/Chisolm Road will dictate the way Main Road is widened. Current alternatives under consideration include widening both sides of Main Road (a symmetrical widening), widening the east side only, and widening the west side only. Once the project team has decided on the intersection improvements, then they can determine how to widen this section of Main Road. 

Identification of Preferred Alternative

To determine the preferred alternative, the project team will continue to refine the reasonable alternatives based on the collection and evaluation of field data. The following criteria will be utilized in order to identify the preferred alternative: 

  • Public Input
  • Cost
  • Future Projected Traffic
  • Jurisdictional Determined Wetlands and Streams (Field identified)
  • Cultural Resources (Field Surveyed)
  • HAZMAT (Phase 1 and 2)
  • Threatened and Endangered Species (Field Surveyed)
  • Right-of-Way Impacts
  • Relocations

USACE will ultimately permit the “Least Environmentally Damaging Practicable Alternative” (LEDPA). The LEDPA is specifically evaluated in regard to aquatic sites, but considers all other natural and built environmental resources, including public interest factors. As such, the selection of a preferred alternative will be based heavily upon impacts to Waters of the United States (WOUS) while considering all other applicable impacts to resources.