In the UK we have camera-controlled variable speed limits which measure the average speed of passing vehicles over 1km
Most drivers slow to about 4mph below the limit in order not to drift over it (easy to do in a 6 mile, free-slowing 50mph zone). I found the best solution to the stress of speed monitoring is to use an android phone as a head-up-display mounted next to the rear view mirror. the Torque app relays car instrumentation to the smartphone display, reading it from the ECU via a bluetooth adapter plugged into the car's management port. i look at the rear view every few moments anyway, now I have a large, bright display giving GPS speed, fuel economy and engine temperature alongside it, in my peripheral field of vision