The London Transport Data blog have details on the rise and rise of 20mph zones across London over the last few years. It shows that some boroughs are really pushing 20mph zones in their residential streets (mostly in the east), while others (mostly in the west) have yet to realise the benefits for their residence.

Find out more at http://londontransportdata.wordpress.com/2011/08/03/update-on-20mph-zones-in-london/