Question to the Department for Transport:

To ask the Secretary of State for Transport, what steps his Department has taken to investigate the effectiveness of 20mph zones in local authorities which have implemented them.

Research into pilot 20mph speed limits, with little or no traffic calming, in Portsmouth and Bristol published in 2010 and 2012 showed small reductions in average speeds. The Portsmouth scheme also saw a reduction in casualties greater than the equivalent national reduction.

Reviews of 20 mph zones in 1996 and 1998 by the Transport Research Laboratory found that zones, which incorporate traffic calming, achieved significant reductions in speeds and annual accident frequency. Reductions in speeds were minimal without traffic calming.

The Department for Transport has commissioned new work into the effects of 20mph limits including effects on speed, collisions, casualties and modal shift. The research also considers best practice, road users’ perceptions and environmental quality.