U.S. 21 Bridge Replacement Over Harbor River

Beaufort County, South Carolina

For more than 80 years, a swing bridge that carried Sea Island Parkway (U.S. 21) over the Harbor River was the lifeline between South Carolina’s Beaufort County and its offshore islands that are popular destinations for tourists. The area also is home to commercial shrimping operations while the river and associated wetlands are rich with marine life, some of it protected by state law. In addition, U.S. 21 provides the only exit off the islands during weather-related emergencies.​​​​​​​

In recent years, the bridge had deteriorated, causing reliability and safety concerns. In 2017, the South Carolina Department of Transportation (SCDOT) engaged Michael Baker for the U.S. 21 Bridge Replacement Over Harbor River Project.

Michael Baker provided design review and construction engineering and inspection (CE&I) services for this 3,350-foot, fixed span, high-level replacement bridge. The scope included public relations and construction management services. CE&I services included project management, document control inspection of the bridge's concrete foundations, concrete superstructure, roadway embankment, earthwork, drainage systems, asphalt paving, erosion control and traffic control, as well as erosion control inspections and reporting. The Michael Baker team also provided reviews of all design submittals, oversight of the environmental permitting, and performed the erosion control inspections and reporting for this design-build project.​​​​​​​

The replacement structure features 12-foot-wide lanes with 10-foot shoulders in each direction. The project also included the demolition and removal of the existing swing span bridge, all appurtenances and portions of the approach roadways.​​​​​​​

Additionally, the project is in a highly sensitive environmental area that includes saltwater wetlands, oyster beds, an eagle nest and habitats for manatees, sea turtles and migratory birds. Serving as the environmental compliance manager, Michael Baker managed the compliance process from design review through project closeout, which included formally documenting and closing out 71 environmental commitments across a wide variety of environmental categories. 

When the new bridge opened in April 2021, the project fully realized the objectives SCDOT had envisioned — smoothly flowing bridge and river traffic, no adverse impacts on local fauna and commercial shrimping and a safe evacuation corridor off the islands. In addition, this vital, complex project was completed nearly 12% under budget.