kyser_soze
Hawking's Angry Eyebrow
The average speed of a car in London is around 2mph. Cars are hardly practical or efficient in urban environments.
average speed for a car ranges from 7 to 12 mph depending on who you ask from the look of it:
http://www.google.co.uk/search?sa=N&tab=nw&q=average car speed in london
The more interesting point is that this has remained pretty constant since the earliest days of motoring - which is an indicator that improved traffic management really does work!!