I've noticed on motorways recently that HGV drivers often try and overtake their colleagues despite having only a 2-3mph speed advantage over the truck in front. With lane one occupied by a truck doing, say, 59mph and lane two by one doing 62, the result is usually tailbacks whilst this pointless manoeuvre is slowly and painfully executed.

Why do they do this? Most trucks are limited to 62.5mph anyway, surely there cannot be that much of an advantage to the driver?