Traffic Signal Terms|
|Please note: This document is a continuation from Part One|
Single Face Heads
Single face heads, also called adjustable face heads, are signals that simply face one direction. They can be post, mast, mast arm or span wire mounted and may be configured as single heads or part of a "cluster" of heads facing two or more directions.
Fixed Face Heads
Fixed face heads, also called fixed four-way heads, are box like signals that have indications on multiple sides, typically all four sides. These signals are typically span wire, mast arm or post mounted, however some have been mounted on the sides of masts, generally equipped to display only two or three directions.
"Two Bulb" and "Three Bulb" Signals
The earliest fixed four-way signals were designed where a single bulb in each section shone in all four directions. This design required that the color arrangement of the lenses for the cross street be the opposite from that of the main street. If the main street had red on the top and green on the bottom, the cross street would therefore have to have green on the top and red on the bottom. In the early days there were no standards for the arrangement of signal indications so the reverse of what we consider today's convention was not unusual. (These signals were still produced until the end of WW-II.)
Three Color and Two Color Signals and Beacons
The first two-color signals appeared in Salt Lake City in 1912. The first three-color signals appeared in Detroit in 1920. Both designs have been in use until the early 2000s when the last known two-color signals were phased out in New York City.
Beacons originally shone yellow in all four directions and simply indicated the locations of intersections in the days before high intensity street lighting. Early beacons shone a steady light and many rural beacons were acetylene powered. In the early days beacons simply indicated a warning. Later red indications were added for cross streets or in all four directions to reinforce stop signs.
Pedestrian signals started out relatively simply. In many instances a simple "WALK" indication by means of a white lens with the word "WALK" masked onto it being added to existing traffic signals or on separate post mounted heads. The idea was that pedestrians should only step off the curb when the "WALK" indication was lit. It soon became apparent that a "WAIT" indication was also needed since pedestrians often didn't notice when the "WALK" indication went dark.
Soon all sorts of pedestrian signal designs were developed using incandescent lamps in modified traffic signal heads, words made from neon tubes and eventually the more common LED "hand-man" configuration that is prevalent today.
(Please note: This feature is still under development and will be expanded.)