Just watched todays “working lunch” on BBC2 and the had a feature on a bridge alert system where you input your vehicle height and if you attempt to go under a bridge thats too low it warns you .
The device works via GPS and has a database of bridge heights in the uk lower than 16’6" no mention of prices but apparently TNT and bus companies are using it, if they will could make the database available and it could be combined with autoroute and GPS that would be worth having , doesn’t say they will but if they have enough enquiries who knows here is the link bridgeclear.com
hope this is of interest