For this project, F.B. Harding Inc. relocated 600’ of an existing 12-way underground duct bank which provides power and controls for four large ventilation fans that serve the southbound lanes of the I-395 tunnel into the tunnel itself. The relocation of the duct bank was to create space for a new residential high-rise project that is being built adjacent to the tunnel on 3^rd St NW. As the tunnel and its infrastructure were built in the early 1970’s, there was little reliable information that could be used for reference. FBH took the lead and worked closely with DDOT (DC Department of Transportation) and their tunnel management team to work through the logistics and unknowns. After the installation of 7,200’ of 4” rigid conduit in the auxiliary lanes of the tunnel and pulling feeder, control and communication wire, the final step was the cutover of all the wiring for the 4 massive fans. This step was of great concern to DDOT as these fans are a critical component of their safety systems. The cutovers went smoothly and finished ahead of schedule thanks to the careful planning and coordination between FBH, the Harvey Cleary team and DDOT.