A person that constantly speeds up and slows down... then speeds up and slows down, causing traffic to act like a slinky being dragged across the floor.
"That Slinky driver needs to pick a damn speed. Yes, your brakes are still there.. Oh.. found your gas pedal again I see"
When all lanes are moving at nearly the speed limit but stuck behind a line of cars with nobody in front of them. Everyone behind the front line of cars are stuck and unable to pass. Usually happens when a cop is in the front and everyone is afraid to pass them.
Thanks to a cop camping in the left lane I was in a rolling traffic jam all the way to work.