KITT, I need you buddy. Sounds like fiction but is not as far aways as one may think. Google is working on a driverless cars for years and also participated on driverless car contests. Recently, Google invested $250M in a taxi service company. And Google already has street maps from all over the world. Combined with a device like Google Glass or an (not presented yet) SmartWatch, it would be not that difficult to design a car which comes to you by calling for it on your device.
Furthermore, Google already has a kind of congestion detector implemented in it’s navigation services. If there are many people using a Google device on the street with GPS activated, Google can easily handle this data and redirect the cars to avoid congestion.