This project focused on the critical replacement of 17 Variable Frequency Drives (VFDs) within Ventilation Building 5, a key component of the Big Dig tunnel system in Boston. These VFDs regulate airflow throughout the tunnels, making it essential to maintain uninterrupted ventilation during the upgrade. The installation involved extensive conduit work, power and motor control integration, and updates to the SCADA system for improved monitoring and automation. Beyond the VFD replacements, the project also included targeted repairs and upgrades to other vital tunnel infrastructure—such as variable message signs, security cameras, emergency radio communications, local field controllers, and real-time traffic monitoring systems. Together, these improvements strengthen the reliability, safety, and operational efficiency of one of the most complex urban tunnel networks in the country.