University of California Transportation Center

About one quarter million intersections in this country had, as of 1996, been fitted with traffic control signals. That number is increasing annually as urban sprawl and increased crowding lead to more traffic and to the need for more vigorous traffic control capability. Each intersection has an average of 40 such signals using either 69 or 150 watt incandescent lamps. Half of these are on at a given time, and due to the existence of protected left turns , the red traffic signals are on the most, perhaps 55-60% of the time. This a large energy burden though of course, the sight seer gazing down on a clear evening at the San Francisco Bay Area from the surrounding hills, would not see these as a predominant source of lighting. Nonetheless, these are an important economic burden to the agencies that maintain them, for those agencies are governmental and a trend in the 1990's towards increasing economic pressure has require them to explore any avenue of cost savings that is available. Of course, seeking efficiency is often prescribed by governmental authorities and thus stands as a required and desirable product of day-to-day operations.