Ah, the A13. You'll see me speed past you at some point around 7 AM and 4PM in the N/S zones. Yeah, unless there are no average speed cameras, I usually go around 10MPH over. Lorry's seem closer because of their size, and don't forget, your mirrors will alter that actual distance to what is actually behind you. Unless you are that guy that does 45/50 in the middle/outside lanes of motorways, dual carriage ways ect, then don't worry.