Transportation authorities across Kentucky have been replacing the incandescent halogen bulbs in stop lights with energy saving Light Emitting Diode (LED) bulbs. In addition to saving energy, the LED bulbs require less maintenance. LED technology has been around for decades; however, only recently have LED prices fallen to such a level where it became cost effective to them in traffic lights.

More information: Courier-Journal: LED traffic signals save money (Nov. 29, 2004) 

(Updated Dec. 22) More information: Kentucky Transportation Cabinet: Light Emitting Diode (LED) Traffic Signals are Being Installed in Kentucky to Reduce Cost and Improve Efficiency (Dec. 21, 2004)