What is the law on 3.5-tonne and 7.5-tonne gross box vehicles in relation to motorway third lane use? The right-hand lane of a motorway with three or more lanes must not be used (except in prescribed circumstances) if you are driving a goods vehicle with a maximum laden weight exceeding 3.5 tonnes but not exceeding 7.5 tonnes, which is required to be fitted with a speed limiter, or by a goods vehicle with a maximum laden weight exceeding 7.5 tonnes. Does this mean that a fully laden 3.5-tonne box vehicle, weighing exactly 3.5-tonne or under, can use the third lane? And a fully laden 7.5-tonne box vehicle weighing exactly 7.5-tonne or under can use the third lane if they are not speed limited?