K.J.
I too have a son who loves signs/lights. Bruder toy company makes large realistic contruction vehicles and several of their extras include road signs, several types of gravel etc. They will send you a catalog. Also, pick up a free playmobil catalog at the nearest toy store. Playmobil extras or "add ons" include flashing hazard
roads signs, numerous types of fencing, lots of worker-men with tiny hand held yield/stop signs and road repair kits.
Forgot to add--google"civil engineers tape" it's a roll of tape (like to size of duct tape) that has a road printed on it. He could design his own roadway on the carpet or a large piece of cardboard.