As I have argued in several previous posts, 20mph limits in residential areas [which is Green Party policy] would _reduce_ carbon emissions, because they would incentivise walking and cycling, the main barrier to increases in which is fears over safety. Furthermore, however, there is an additional crucial argument in favour of 20mph limits: Most cars hitting 30mph in residential areas will be doing so through fast acceleration and deceleration, which is highly inefficient fuel-wise. The argument in favour of 30mph rather than 20mph limits is predicated upon tests of fuel-consumption WHEN DRIVING AT A CONSTANT SPEED. But constant driving at 30mph in residential areas is very rare [and when it happens, is rarely safe!]. Constant driving at 20mph is far more plausible – and less fuel-inefficient than rapid acceleration and braking. -- Rupert Read Green Party Councillor, Norwich, and Lead Candidate for Eastern Region for the Greens in the 2009 Euro-elections. Why not try my new BLOG...