“The majority of the world’s population already lives in cities, and by 2030, this number is predicted to grow to 5 billion. Globally, it’s estimated that by 2050, 75 percent of the population will live in cities. Already, cities and regions ranging from Jakarta, Indonesia, to New York are bedeviled by gridlock and underfunded infrastructures. Moreover, transportation already accounts for 28 percent of U.S. greenhouse-gas emissions, and the number is rising. Transportation is also costing us even more: At the turn of the 20th century, U.S. households spent about 2 percent of their income on transportation. That figure is now around 18 percent, and it’s also rising. And then there are the other social costs, not just time lost in congestion but the larger cost in human lives: The World Bank estimates that by 2030, road deaths could become the fourth or fifth leading killer worldwide, a larger threat than malaria.”