Normally, traffic signals operate 24 hours a day, seven days a week, 52 weeks a year. The signals direct traffic through intersections, only requiring periodic maintenance and a power supply. However, when the power is interrupted, the signals no longer can function as intended. In Louisiana, as with most states, when the signals are dead or inoperative, they revert to all-way-stop operation — leaving it up to drivers to be the traffic cops.
When traffic levels in the affected intersection exceed 20,000 vehicles per day, the result is mass confusion bordering on anarchy. Usually, one direction tends to dominate the flow of traffic, as one driver spurs the rest of the drivers in the group to go until vehicles from another direction take control. The end result is a strong potential for accidents.
In June 2006, the city of Shreveport, La., began to research the use of backup power systems for traffic signals. Shreveport's location subjects it to high summertime temperatures and freezing conditions in the winter, resulting in potentially strong storms, high wind speeds and extended downtime due to power outages. The city was interested in installing a safeguard that would keep the traffic signals operating during such power outages and that would handle the seasonal extremes.
When city officials were researching power backup systems, it became clear that battery backup systems were the only type of system available on the market at the time. Such systems typically ran for about four hours. In addition to the short runtime, the power supply was incapable of running the video camera systems for the city's intelligent transportation system (ITS) operations. In short, the signals would run only with the preemptive time sequence and only for four hours.
As city officials began to investigate other means of providing a power backup for the signals, they considered the use of natural gas generators. In talking with most generator suppliers, however, city administrators determined that natural gas generators could not meet the city's needs — which included smaller Kv generators, automatic on-off switches and a means to monitor the system. The suppliers only wanted to supply larger systems with some of these capabilities.
At this point, the city began discussions with a local company that provided power backup to commercial businesses. City officials met several times with Randy Smith of Power Up Electric to discuss the city's requirements. As a result of these meetings, Smith's company designed a system called Auto Traffic Cop.
Auto Traffic Cop on the beat
Auto Traffic Cop is a self-contained natural gas system that provides continuous backup power for traffic intersections. The Auto Traffic Cop units usemonitoring technology to check the system's health every six seconds, to perform automatic exercise cycles each week, to send run and stop reports and to communicate other important information. Thanks to the GPS modules, users can access system data from any location via the Internet.
Initially, the city installed three Auto Traffic Cop units, and the units operated exactly as predicted. Due to the high success of the first three units, the city installed an additional 17 units and is in the process of installing an additional 30 units. The unit is now spec'ed as standard equipment on new signal installations.
Auto Traffic Cop can operate all signal and camera operations at full power to maintain the ITS capabilities for the intersection. City officials have concluded that Auto Traffic Cop is cheaper than the battery backup systems in terms of the initial cost and the routine maintenance costs.
Auto Traffic Cop's monitoring system allows city officials to know when the units are running — a feature that already has proven to be valuable. At one location, the system ran for 16 hours due to a power outage. Because the power circuit only had streetlights and traffic signals, the power company received no calls from businesses or citizens due to the outage until the city notified the company as a result of the generator reporting the outage.
Bossier City, La.-based Auto Traffic Cop provided this case history. The views and opinions expressed in this case history do not necessarily represent those of Government Product News or Penton Media Inc.
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