I assume you're talking about the 47mhz channels... For the most part, yes. For flagging and traffic control, they use the 156mhz portables. Some folks have heard other low power channels, but I haven't. (I've even heard and seen flaggers using FRS radios occasionally).
Actually, the 47mhz channels aren't quite as busy as you'd imagine, even here in the Charleston area - except, of course, during bad weather. I don't know where you are, but make sure you have all seven (eight???) of them programmed in. They have been known to change districts...