This article describes the significant cost savings and other advantages obtained from using light-emitting diodes (LEDs) in traffic signals. The US Department of Transportation estimates that the USA's 260,000 signal-controlled junctions, with about 5M traffic lights, use more than 500MW of electric power. The energy cost of a large signalised intersection can exceed US$3000 per year. The energy consumption of a typical LED traffic light is just under 10% of the consumption of a conventional traffic light. The cost of converting red signals to LEDs can be recovered in two to three years on energy savings alone. LED efficiency has improved dramatically during the last 25 years. Important installations of LEDs in traffic signals have already been made in parts of the USA. In 1991, the city of Sparks, NV began to test LED signals. In 1996, Denver, CO began to replace about 17,000 incandescent red and orange signals, at a net saving of more than US$5M, assuming a life of 100,000h for a LED light. The State of New Jersey recently converted nearly 1000 junctions to LED signals. Philadelphia, PA is now converting traffic signals at all its 2900 junctions. The California Department of Transportation (Caltrans) estimates that over US$105M per year could be saved by converting all traffic signals in California.
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