I also know what 30mph feels like when driving. Surely to drive within the speed limit you don't have to stare at your imperial speedo all the time, do you? The easiest way to avoid being caught by speed cameras is not to speed, then you don't have to care whether they are there or not! What anti-speed camera campaigners would be better of doing is sorting out the discrepancy between being fined for doing 32mph in a 30 limit when car speedos are only supposed to be accurate to +/-10%. The obvious answer there is to drive so that at +10% of your indicated speed you are still within the limit, but that's pushing it a bit!