When the General Motors EN-V concept vehicles were demonstrated at the 2011 Consumer Electronics Show http://bit.ly/u69R8R and http://bit.ly/tNtRpU, one of the most frequently asked questions by the media was "when will we see something like this hit the streets?"
Christopher Borroni-Bird, GM's director of advanced technology vehicle concepts explained that small autonomous vehicles like the EN-V were probably at least ten years out. One of the limiting factors is the accuracy of current GPS systems. Right now the satellite based location system is can pinpoint a location down to about 3 meters (all bets are off if you are in an urban canyon in a place like Manhattan or Chicago). Reliable autonomous operation will require sub 1-meter positioning so that vehicles can stay in their lanes and better performance in dense urban areas that these vehicles are best suited too.
Borroni-Bird mentioned a new generation of GPS satellites that would be put into orbit later this decade could resolve this problem. Lockheed Martin is about to take a big step in this direction as it starts testing the first of these new satellites in preparation for launch in 2014. http://bit.ly/sNAbBl