Alternate power source keeps traffic lights operational in Sugar Land

Tommy Haynes
Director of Public Works
City of Sugar Land, Texas

Many motorists take for granted the importance of traffic signals in their daily commutes and how they are essential in regulating the safe, orderly flow of traffic throughout the community. These electronic marvels are pretty much ignored until they stop working. When this occurs, motorists become confused, the movement of traffic is impaired and the chance for accidents significantly increases.

The City of Sugar Land recently implemented a system that has dramatically improved mobility and safety throughout the city. In order to restore operation of traffic signals during extended power outages, the city's traffic signal control panels have been retrofitted to quickly accept an alternate power source that allows the use of a portable generator unit.

Simple to operate
Other cities have used generators to power traffic signals, but Sugar Land's concept is different because a connection is built into each signal cabinet that eliminates the need for a technician to physically disconnect the power supply—the service cable. Disconnecting service cables and installing jumper cables to power an intersection with a generator is time-consuming and exposes technicians to electrical hazards.

Sugar Land's signal cabinets are able to accept an alternate power source via a power relay hookup. When the generator is started, it powers the relay in the signal cabinet and powers the intersection. When the generator is disconnected, the relay falls out and switches back to the traffic signal's normal power. It's just as simple as plugging an appliance into a power outlet.

Rapid response
To ensure timely responses to traffic signal outages, the Sugar Land Traffic Control Division designed and built an emergency response unit capable of distributing a generator to a location in a matter of minutes. The response unit is also equipped to provide refueling of the generators to ensure uninterrupted operation for extended periods. The unit—a custom trailer that can hold up to six generators—is ready to roll 24 hours per day and attaches to any Sugar Land Public Works vehicle. The trailer includes a 40-gallon fuel tank with a pump, as well as toolboxes to carry tools, chains, connecting cables, etc. The trailer's most impressive feature is a boom with a chain hoist that enables a single technician to deliver and install a 250-pound generator. The concept was the product of the city's Y2K efforts, which included two trailers loaded with generators to ensure that the city's traffic signals operated in the event of a catastrophic power failure throughout the greater-Houston area.

Public safety
A recent study completed by the Sugar Land Traffic Operations Division determined that more than 70 percent of the City's traffic signal failures are due to electrical power loss, which are attributed to a number of factors, including:

  • Severe weather;
  • Accidents that damage power poles and lines; and
  • Construction due to development within a community.
Contingent upon the severity of the damage, restoration of electrical power can take a significant amount of time. During this period, police and traffic personnel are dispatched to manually direct traffic and install signage until power is restored. Traffic signal outages consume a significant amount of resources and normally occur during severe weather conditions that require the deployment of public safety employees and other resources to protect life and personal property. The use of the traffic signal response unit has proven to be a major asset in minimizing traffic congestion and enables police officers to spend their time protecting citizens.

The alternate power source and rapid response unit also drastically reduces the need to expose Public Works employees to dangerous working environments, including dark, wet intersections.

Initially, the city tested the concept of powering intersections by manually wiring the generators to signal control panels; however, this approach was time intensive and exposed personnel to potential hazards. Shortly after the city began studying the alternate power source for traffic signals, a storm caused an intersection in Sugar Land to go dark during morning rush hour. Because it was raining sideways, the decision was made not to install a generator. The wet environment was not safe for technicians or the city's assets—it was like taking a bath with a toaster. This was the selling point for the retrofitting of Sugar Land's signal control panels. The city approved funding for the purchase of seven 4,500-watt generators with 30-amp circuits.

Sugar Land is no longer at the mercy of the power company when it comes to signals outages. Mobility has definitely been improved immeasurably; instead of an all-way stop during a power outage, motorists pull up to a signal that is operational. Their house may be dark when they get home, but the signals are running.

Tommy Haynes can be reached at (281) 240-7412 or at