During World War II, the government encouraged carpooling because they needed the gas and rubber for the war (source). Here is a sample of the propaganda:

This one is, as it appears, by Dr. Seuss:

The next two are from the State of Ohio:

In the comments, both Eoin and Toban B. (T.B.) pointed us to this poster (found here).

Lisa Wade, PhD is an Associate Professor at Tulane University. She is the author of American Hookup, a book about college sexual culture; a textbook about gender; and a forthcoming introductory text: Terrible Magnificent Sociology. You can follow her on Twitter and Instagram.