40mph hero
A person who never exceeds forty miles per hour, even on long straight roads, in clear conditions which have a higher speed limit. The same people will often stay at 40 even in lower speed limit areas. They are one of the most frequent causes of delays, road rage and dangerous overtaking.
"Sorry I am late, I got stuck behind a 40mph hero" or "I was about to cross the road when I almost got ran over by a 40mph hero"