Commuting on Maryland freeways I normally put the car on cruise control right at the speed limit, and stay about 150 yards behind the car in front of me. There is no point speeding because you will get pulled over and you will hit a traffic jam further up the road.
What I find is that many cars pass me, and then pull their Prius (or other small piece of crap car) back into my lane only 10-15 feet in front of my SUV. The only reason I can think of to do this, is a death wish. Does anyone believe that a car going 60 MPH can stop in 10 feet?