INNOVATION IN TIME OF CRISIS: Inverters to Temporarily Power Traffic Signals
By Pinellas County Public Works – Transportation Division Clearwater, Florida
On Sept. 8, 2017, the Pinellas County Emergency Operations Center fully activated as Hurricane Irma began to track toward the state of Florida.Pinellas County, located on the west coast of central Florida, was directly impacted as Irma passed through on Sept. 10 as a Category 1 hurricane. An estimated 321,053 people were affected by mandatory evacuations and over 23,000 were sheltered. The high winds up to 90 mph, and heavy rains affected a large portion of the county.
Resident and visitor safety was the utmost priority including basic necessities such as water, healthcare and power. The aftermath left over 422,000 residents without power anywhere from a few hours to over a week. And while the damage to the transportation infrastructure was not great, Pinellas County did sustain considerable damage to the power grid resulting in heavy power losses to traffic control lights and warning systems throughout most of the county. This included loss of power to a minimum of 148 of the 365 traffic signals maintained by the Pinellas County Public Works’ Transportation Division. The Pinellas County Sheriff’s Department provided traffic control manually at 75 intersections the day after the storm. For larger signal locations, as many as four deputies and four police cruisers were required at a single intersection to safely control traffic.
A coordinated effort was organized by the Public Works’ Transportation Division with the Pinellas County Sheriff’s Department and local municipal law enforcement agencies immediately following Hurricane Irma to address these traffic signal outages, especially those at major intersections. The County utilized Uninterruptable Power Supplies (UPS) at over 240 major signalized intersections, which were turned off prior to the storm with the intent of powering up the signals the following morning to cover the gaps in power. The 4-6 hours of battery life supplied by the UPS was not sufficient for the long-term outages that were occurring. The small number of generators that were supplied by the Florida Department of Transportation (FDOT) and the Emergency Management Department only covered approximately 17 critical intersections and carried their own maintenance and operational issues.
To supplement the available power options, an initial assessment was made along with the decision to implement the use of the recently designed field inverters. These inverters were specifically developed to provide a quick, temporary power source to traffic signals during power outages. The county deployed and monitored these temporary power supplies at strategic intersections until the county’s power was fully restored. Pinellas County Public Works’ Signal Shop installed the first inverter at a key intersection located at McMullen Booth and Sunset Point Roads. This installation not only provided the temporary power source to the intersection’s affected traffic signal, but also allowed law enforcement, who would normally direct traffic flow under the circumstances, to remain safely out of the flow of traffic. With the success of the first inverter placement realized, the Signal Shop staff proceeded to use available parts and purchase additional inverters to assemble additional units to be used in the field at various locations. The newly-constructed inverters were positioned at major county intersections, allowing a portion of the assigned officers for these areas to be utilized for other emergency duties. As each intersection regained power, the inverters were then moved to traffic signals that had not yet been repaired – allowing the transportation team to “leapfrog” them throughout the county and continue the temporary fixes until power was fully restored to all affected traffic signals.
The following information provides the technical details and instructions on how the inverter can be constructed and used for temporarily powering traffic signals. Since LED modules use up to 70% less power than previously used incandescent lamps, the electrical current draw at the traffic signal is reduced to a level that can be powered by a standard 1800 watt inverter. A UPS is necessary to provide a supply of “clean” power and experience has shown that a standard inverter should only be used at locations with a UPS.
This solution has well-defined criteria:
• the intersection was equipped with LED modules;
• the intersection contained an uninterrupted power supply (UPS); and
• the inverter-equipped vehicle remained running onsite until the permanent repair was completed.
The construction of inverter units requires the following basic components, which can be purchased from home improvement or auto parts stores:
• 1500 watt inverter (minimum)
• Heavy-duty jumper cables
• Tool replacement cord
• 30 amp Twist lock connector
• Eyelet connectors
1. Cut the jumper cables in half; this provides ends for 2 inverter sets.
2. Cut and crimp the eyelet connectors to the wires and connect them to the inverter.
3. Take the replacement cord and connect it to the 30 amp twist lock connector, or the UPS connector type used by your agency.
4. Connect the plug of the replacement cord into the inverter and connect to the UPS.
5. Connect the jumper cables to the source vehicle that will be supplying the battery power.
6. Monitor the inverter and the intersection.
As the storm passed and the county’s first responders were activated, including the Pinellas County Public Works Department, roadway safety was of the utmost importance to begin recovery efforts. The use of the field inverter units during this time of crisis resulted in the successful usage of temporary power sources for traffic signal outages; provided the efficient use of Public Works and Sheriff’s vehicles; increased roadway safety for first responders and county residents; and established a valuable collaboration with local law enforcement.
This use of inverters by the Signal Shop staff to power intersections had been used successfully in the past. Temporary signal outages were remedied by powering the signals with Public Works standby signal response vehicles equipped with these inverters, making the intersections fully operational until a permanent repair could be made. However, the expanded use of this equipment on a larger scale and inclusion of this additional tool as an integral part of the emergency response scenario was an insightful step forward.
Pinellas County is currently evaluating this new technology option and is actively examining how this model can be optimized, shared with law enforcement agencies, and incorporated into solutions for routine traffic signal outages as well as in times of emergency.