The world is rapidly motorizing. At the start of the twenty-first century, some one billion vehicles occupied the roads. But this number will likely double in the next decade. By mid-century the Earth could be home to billions more cars, trucks, and motorized two-wheelers, which will collectively have profound effects on global oil demands, energy security, climate stability, and urban mobility.

We are at a critical crossroad. The global proliferation of vehicles presents many risks and opportunities. One seemingly easy way forward is to adopt last-century approaches that seek to accommodate the high demand for vehicles through cheap oil, free roads, sprawled development, and subsidized home ownership. A preferred alternative course beckons, however, one that promises new, low-carbon, location-efficient, economically productive mobility. Government, industry, and consumers—especially in emerging economies—can reinvent transportation models and employ innovative solutions to avoid a foreboding car monoculture.