A convoy of 20 trucks and two halftracks. Look how much road space just this small convoy takes up. Imagine an entire tank battalion of 100 tanks and as many other vehicles. No wonder the military police are so essential when units move.
Some say airplanes should not fly along the road when they attack a convoy, but rather should attack it from the sides. An attack along the road may cause you to be more likely to fly over an exploding truck and knock yourself out of the sky.
Proper spacing between vehicles is essential. You don't want one large mine or bomb to explode and take out more than one truck. On the other hand, more distance between trucks makes it hard to keep together in poor visibility or to respond to infantry ambush.