In many urban areas, a third of the cars on the road have already reached their destination and are just circling the block waiting for a parking space. This leads to a cascade of problems, including pollution, traffic congestion, and accidents. Now massive arrays of networked sensors installed in city streets could significantly improve the situation by helping drivers find parking spots quickly.

"We're trying to make it really easy for people to find a parking space," says Jay Primus, who manages San Francisco's new SFPark program, the most advanced smart parking system in the United States. The city has recently installed magnetic sensors into the asphalt beneath 8,200 street parking spaces and is also collecting information on thousands more parking spots in garages, as well as from smart parking meters. All that information is linked to a central management system. Drivers can use a website or smart-phone app to access real-time data about where parking is available and how much it costs.