Uninterruptable Power Supply / Battery Backup for Traffic Signals

About the Program

Category: Transportation (Best in Category)

Year: 2017

Montgomery County DOT has recently completed they deployment of uninterruptable power supplies / battery backup units (UPS/BBU) for all County owned traffic signals. There are over 320 of these devices installed in the field. This work was undertaken as part of a larger capital improvement project for modernization of the County’s traffic signal system. The decision to install UPS/BBU at all County owned traffic signals was made to address the following issues; 1) improve public safety by keeping traffic signals on color during temporary short term power outages, 2) keep critical communication hub sites powered so that a power outage won’t disrupt communications to other traffic signals connected to that hub and 3) reduce the need to dispatch police officers and signal technicians for short term power outages. In addition to installing the UPS/BBU at traffic signals, they are equipped with communication ports that permit the County’s Transportation Management Center (TMC) to remotely manage and monitor these devices. When the power is lost at a traffic signal, the UPS/BBU instantaneously switches to an inverter powered by batteries to keep the signal on color. The TMC is notified immediately when the power goes out at any UPS/BBU equipped traffic signal. The County designed these devices to provide a minimum of eight hours of battery backup power which will keep the traffic signals on color for the duration of the vast majority of power outages experienced. In addition, the UPS/BBU will protect the traffic signals from under or over voltage. If utility voltage gets below a set threshold, the UPS/BBU will boost the voltage back by supplementing with the inverter. If the utility voltage goes over a set threshold, the inverter will bring that voltage back down to a safe level to protect the signal control equipment.