Rush hour in Copenhagen is dominated by people on bicycles: Around two-thirds of the city’s residents now bike to school or work instead of driving. That wasn’t an inevitable reality: Bikes were popular in the city early in the 1900s, but by the 1950s, as people got richer and moved to the suburbs, cars had overtaken bikes on roads.

By the 1960s, city planners saw cars as the future and bicycles as outdated. They sketched visions to add new urban highways and take out bike lanes that some thought were a waste of space. But the global oil crisis of 1973—when oil prices quadrupled within a few days—helped push the city in a different direction…

As Denmark confronted its dependence on foreign fossil fuels—when the oil crisis happened, imported oil covered 80% of its energy needs—it looked for ways to generate electricity and heat differently and to drive less.