How many times has this happened to you? You’re in the left-hand lane, cruising smoothly down the highway at 70 miles an hour, and then all of a sudden, traffic slows down to 30 miles an hour. Then it speeds up again before grinding to a halt again—and this pattern continues over and over, much like the action of an accordion. Eventually, you see why. There’s an accident on your right-hand side and cars are stuck everywhere.