There's no right answer but there is an easy solution. Take the safest option at the time. They teach yer not to pull out to overtake if yer not overtaking. So following a truck into lane 2 to overtake at 1mph faster isn't really worth it. In this situation you either stay behind the 50mph truck in lane 1 which is a risk in itself, or don't use the motorway if yer want to drive below the average traffic speed. I know the highway wombles do it but they're looking out for crap on the roads. The easy solution is not to drive slower than general traffic so yer don't put yerself in this situation, or stay off the motorway. Peeps changing lane is probably the most likely cause of bumps on the motorway. Pulling out or into someone else. If you drive slower than everyone else you create a bubble of over takers around you all the time. The bubble zone has a higher risk of bumps.