beltway bitch
a motorist who refuses to match the prevailing velocity of other motorists on a high-capacity arterial roadway, often in heavy traffic; a motorist who is driving too slow in the fast lane; a motorist who hogs the fast lane when others are passing on the right; a motorist who is impeding traffic. Often, the offending motorist lacks confidence in his/her driving abilities, fears other drivers, or has been deluded into thinking that by going slow on the freeway, s/he is making the world a safer place.
That beltway bitch is going way too slow. He is going to cause an accident!