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 Departme

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.