One possibility is companies that make electronic devices for this; not all of it is classical embedded, BTW, or at least so I remember from one small company I

One possibility is companies that make electronic devices for this; not all of it is classical embedded, BTW, or at least so I remember from one small company I interviewed at which used Visual Basic in the '90s and at least a bit beyond, although I can't remember exactly what they were doing. That won't be traffic engineering per se, but will be a part of it. Various units of government with responsibility for high traffic and congestion road system set up command centers of a sort, with lots of cameras, the ability to change signaling systems, put messages up on signs, maybe even open or close entrance gates and the like. In the center I worked at for a while (on their abandoned bespoke software), they also dispatched or coordinated with crews to do work. Which brings up one issue, working for or with the government has its own special characteristics, and is going to be inevitable in this sort of career. Good luck!