I think your comment about the work appearing to be finished (and I've been through that area, too) pretty well defines the problem. Drivers who speed through a work site where there are people working should be charged with endangerment & jailed on the spot - but the problem is that there are so many signs posted, but absolutely no indication that there's any work being done, (sometimes I'll see a sign saying "end work zone" - but it's the first sign I've seen!), that people begin to disbelieve the signs, which is a bad idea. I've often thought that states that use the flashing lights on the signs, to indicate an active work zone, have the right attitude. I absolutely want to slow down in a work zone, because I've stood on the shoulder, & know how scary it is to have even four wheelers zooming by, much less the big trucks, & I sure don't want to endanger someone who's doing their job, because I don't want anyone endangering me - but neither do I want to drive at 45mph for miles for no apparent reason. Particularly when no one else is!
Flashing lights to indicate a need for compliance with the lower speed works in school zones, & I think it would work for construction sites too. Of course, I also think that common sense isn't a job requirement for any state official, so I'm not expecting anything to change. :+