DESCRIPTION: The existing SC 412 (Rainey Road) bridge over Tributary to Big Generostee Creek is a posted, load-restricted bridge located approximately 5 miles west of Starr, SC. The roadway consists of two 9-ft travel lanes and substandard horizontal and vertical curves and is within prescriptive right of way. It also does not meet the 2-ft freeboard hydraulic requirements for the design high water. There are also several utilities with prior rights including transmission lines which cross over the roadway and bridge.

CHALLENGES: The transmission lines, owned by Santee Cooper and Duke Energy, are FERC/NERC regulated and provide power to Georgia Power.  The companies stated a 20-ft setback zone from all conductors and transmission structures is mandated for non-qualified personnel. De-energization of only one line at a time for each owner may be possible and within specified dates. Also, a minimum vertical 35-ft clearance zone is required to the lines and this zone fluctuates based on the energy produced and the temperature.

RESPONSIBILITIES: J. Bragg Consulting prepared the design criteria for a 45mph design & posted speed since this roadway does not currently meet the minimum standards for a 45mph posted speed limit.  J. Bragg Consulting also assisted in the development of the bridge alternatives report by developing conceptual horizontal and vertical alignments. Since the existing bridge is in a sag vertical curve, it was determined to mimic existing conditions while meeting current standards was the best solution for the vertical alignment, and the proposed vertical alignment applied to all three bridge replacement alternatives with minimal changes based on structure type. For the horizontal alignment to meet the design criteria, approximately 900 LF was realigned to eliminate substandard curves. Conceptual plans and cost estimate were prepared. 

It was recommended to replace the bridge with a box culvert to minimize the constructability issues associated with the transmission lines crossing the roadway.  Preliminary plans have been prepared for a triple 9’ x 10.47’ box culvert and submitted for review. 

J. Bragg Consulting prepared right-of-way plans and final construction plans. These included roadway drainage design, erosion and sediment control plans, traffic control plans (detour), etc.  The firm also developed the MS4 Permit package and will coordinated with the hydrology & hydraulic design engineer for additional information associated with the FEMA model.