Ever wait forever in a traffic jam, only to find that when you finally get clear there was no apparent reason for it? You might have experienced a phantom traffic jam. William Beaty performs some traffic experiments and talks quite eloquently about how to help the situation.
I distinctly recall my father, while on our annual pilgrimage to the east coast, always did what he called "pacing". Being a mathematically (and otherwise) intelligent man I think he came to the same conclusion that others have: a smooth flowing line of traffic will move more cars.
So if you find yourself stuck in a jam, try to leave some extra space in front of you - by doing so you will allow your braking to be less severe and thus cause fewer people behind you to spread the wave of stopped traffic backward.