Clearing the roads of four out of five cars has momentous consequences for cities, by measures such as environment, traffic, efficiency, and even parking. In most cities, for example, designated parking accounts for a huge amount of land, which ends up being useless for most of the day. With fewer cars, much of this space could be freed for other uses. Such reductions in car numbers would also dramatically lower the cost (and related energy consumption) of building and maintaining the roads. One engineering study found that automation could quadruple capacity on any given highway. And, of course, fewer cars also means less noise and a smaller environmental impact.