What's the speed limit?

It is one thing setting up an average speed limit over the length of some long-term roadworks and policing this speed limit with average speed cameras, it is quite another to not clearly state what the speed limit is.

Take a trip through the roadworks on the A40 leaving London at Gypsy Corner where the new road bridges over the railway has been being built for some time now and will be for quite a while to come. Currently the speed limit is advertised over the 400 or so yards of the average speed check as both 20mph and 30mph. A mixture of signs means that some motorists are sticking to 30mph and some to 20mph with obvious problems resulting.

Is it too much to ask for some sense in the signing of speed limits, or is this another way of deliberately raising money through driver confusion? Either way the current situation is dangerous as drivers drive through the roadworks with one eye on their speedometer.