And cyclists hate them because they don't trigger the sensors.
The systems would need to be upgraded at cost to us taxpayers, would need careful programming, and central override to cope with exceptional circumstances, such as the sheet ice event a few years back when within 30 minutes roads became covered in up to 1" inch of ice. This M5 junction was an example of that, the A491 (turn left) stopped because it goes immediately into a steep downslope, so nothing could move on the roundabout, and consequently backed up to the previous junction in L1 and L2. I managed to avoid the first, but then got stuck for 3 hours at J5, which is an alternative route, as the trucks tried to get down the slope - but had to wait until the complete slope was clear before attempting it, as just stopping from absolute crawl was enough to get their loads sliding sideways. What really is a bugger about the whole situation is that 50 yards down the J4 slope is a depot for gritters!
The better approach has already been tried in Holland and some other places, and consists of removing all traffic control measures entirely including all lights, most signs, curbs, lines, etc, and just let
all road users get on with it. Hans Monderman is the guy pushing the ideas, and it really works for central urban areas (it also works naturally for failed lights). Try these references:
http://www.wired.com/wired/archive/12.12/traffic.html
or a few of our previous discussions (with other links):
http://www.safespeed.org.uk/forum/viewtopic.php?t=5329
http://www.safespeed.org.uk/forum/viewtopic.php?t=8792