Thanks to plate tectonics, the United States is drifting west at about a centimeter per year. (The people who live there, on the other hand, are on average drifting west at about a centimeter per minute.)
There are 212,309,000 licensed drivers in the US, and since we have more cars than drivers, we can in theory get them all behind the wheel at once. The average car on the road weighs a hair over 4,000 lbs, so we have 850 billion pounds of car (plus around 30 billion pounds of driver) to throw around.
The North American plate, by comparison, is about 25 million square kilometers in area and probably averages around 35 kilometers thick. Given a density of about 2.7 kg/Liter, its mass is probably in the neighborhood of 2.3∗1021kg, so it outweighs our fleet by a factor of about six trillion.
via xkcd
