Slides by Rod King of 20's plenty for us looking at the revisions proposed to DfT circular 01/06 on speed limits in the light of the Portsmouth whole city 20 mph project.

Report by WS Atkins for DfT. 29 September 2009. The conclusion that you could draw from this report is that default 20mph isn't worth the effort but the report looks at speed and casualty figures only and not the wider picture.

Presentation to parliamentary committee by 20's Plenty for us