Have you ever looked for a parking spot in downtown San Francisco?
In 2011 the city invested 20 Mio US$ to equip 19.250 parking spots with sensors that indicate availability to smart-phone users. The solution gets enhanced this year by the feature of parking fares depending on demand-and-supply. If there is a lot of availability parking is cheap and vice versa.
(Source: Robert Thielicke, Technology Review, January 2013, pg. 38)