The first city in the UK to introduce 20mph limits on almost all residential streets has seen the best results on roads where the council disregarded government guidance.
The Department for Transport (DfT) has indicated that interim results of Portsmouth City Council’s scheme would strongly influence new guidance on speed limits.
Last March, Portsmouth completed a nine-month programme to implement signed-only 20mph speed limits on 410 of its 438km road network. A new report commissioned by the DfT has revealed that on roads where the average speed before the scheme was above 24mph, a reduction of 7mph was achieved. This change was described in the Atkins report as ‘statistically significant’.
Current DfT guidance advises that engineering measures are required on 20mph roads where average speeds are 24mph or above. Speaking in Portsmouth this week Duncan Price, branch head of road safety at the DfT, said the results were a ‘key contributor’ to the draft new circular, which would be published at the end of the year. He said there was ‘general support’ for a ‘substantial expansion of 20mph areas’.
The overall average speed reduction in three of the six areas studied was 0.9mph. The report also found accidents dropped by 13%, and the number of casualties by 15%. It has not yet been possible to assess the impact on traffic volume.
Simon Moon, Portsmouth’s head of transport and street managements, said: ‘This interim report is limited in what it can say about the 20mph scheme – we’ll have to wait until it has been running for three years before we get the full picture.
‘But there are some encouraging signs in it, especially the result on roads where speeds were significantly higher than 20mph when we imposed the new speed limit.’ More than half (56%) of KSIs (killed and seriously injured) in Portsmouth occur on residential roads.
The cost of the scheme was £570,000 –about half what it would have cost with additional engineering measures. Oxford is the second city to follow Portsmouth’s lead, with signed-only 20mph limits implemented on all residential roads and some strategic routes at the beginning of September. Geoff Barrell, Oxfordshire CC’s head of road safety, said the scheme was brought in all at once, to make it ‘as politically significant as possible’.
Norwich City Council has delayed the roll out of its proposed 20mph speed limits across the city until the DfT issues the new guidance. The London boroughs of Islington and Southwark, meanwhile, are poised to implement borough-wide limits.
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