Though the global population shows signs of heading for a plateau, the world’s cities continue to grow. Urbanization means the equivalent of a city with the population of New York is now added to the planet every two months. Cities are all about increasing human opportunity by reducing the space between humans, as well as their businesses, homes, schools, and cultural institutions. Cars and trucks — and there are 1.475 billion of them on Earth now — require vast amounts of that precious space. The simple truth is they barely fit into today’s cities, let alone into the megacities of the future.