100 years ago, if you were a pedestrian, crossing the street was simple: you walked across it.

Today, if there’s traffic in the area and you want to follow the law, you need to find a crosswalk. And if there’s a traffic light, you need to wait for it to change to green.

Fail to do so, and you’re committing a crime: jaywalking. In some cities — Los Angeles, for instance — police ticket tens of thousands of pedestrians annually for jaywalking, with fines of up to $250.

To most people, this seems part of the basic nature of roads. But it’s actually the result of an aggressive, forgotten 1920s campaign led by auto groups and manufacturers that redefined who owned the city street.