You don't often see it to that extreme. But I think it's just human nature, when you get behind somebody, to sort of speed up. And it's human nature, when you don't have anyone in front of you, to take it easy. That's one reason I like having a speedometer on my bike, so I can sort of keep a steady pace when passing people, instead of speeding up and slowing down.

People drive like that too, sometimes, gets irritating. Cruise control helps.