One way in which Thorpe tried to combat was trialled on Saw. Basically, the cameras which oversaw the queue line had some software installed (I believe it was called Headmapper or similar). As the name might suggest, this maps people's heads as they go through the queue, and can log how long they're in the queue for. This can also take into account Fastrack and RAP systems, and work them into it. This can then throw up a very accurate estimated queue time based on how many people are in the queue. You may have seen this actually; the queue time for Saw was advertised to the minute (eg 53 minutes) during these trials.
In my experience, this technology was largely accurate, but has some problems:
-It needs constant, full coverage of the queue line (ie: cameras have to be in a fixed position and can't move, and can't have other things to focus on). Most cameras at any theme park will be focused on safety critical areas (parts of ride areas and pathways), with queue lines only in view at the side / background.