A previous post was correct. There width is a standard rackmount in 332-type cabinets. The 332 type cabinets were originally designed by the California Department of Transportation. A lot of the design of cabinet dates back to the 70's. Until just recently the industry started to look at shrinking things down. Going to LED signal indications has helped a lot. The devices used to convert the low voltage coming from the traffic signal controller to switch to the high voltage driving the old incandescent heads took up a bit of space. How you land all the wires from signals heads and sensors also takes up a bit of space.
Some day when we have connected vehicles, vehicles talking directly to the signal cabinet we should be able to shrink things down even more.
Some day when we have connected vehicles, vehicles talking directly to the signal cabinet we should be able to shrink things down even more.