On packed subways and crowded highways, billions of people participate in a short-distance population shift twice a day: the rhythmic ritual of the daily commute to and from work.

More than 300 million people use the United States’ transport systems every day, and in 2012 a whopping 76 percent of them got to work by driving alone, a U.S. Department of Transportation report out last week noted. That can make for a lot of gridlock.