The pilot scheme was tested on 25 miles of streets on the south side of Edinburgh last year, and initial results show there were fewer accidents in the trial area and better conditions for walkers and cyclists.
Edinburgh council is now considering extending 20mph zones to all residential and shopping streets and even some main roads, which would be the first scheme of its type in the country.
Transport Scotland, the government’s transport agency, said once the trial had been fully evaluated it would advise other councils on how to replicate Edinburgh’s success.
However, though safety experts said compulsory 20mph zones were vital in cutting casualties and encouraging commuters to cycle, motoring groups said introducing them on too wide a scale could be counter-productive, especially if main roads were included.
The campaign to reduce speeds follows significant improvements in the safety of motorists and passengers due to better vehicle and road design. Consultants now warn the number of pedestrians and cyclists killed or seriously injured will overtake the casualty toll for those in cars within a few years.
Although advisory 20mph zones have already been introduced in many urban areas, compulsory zones are still relatively rare. Edinburgh City Council said it had received “positive feedback” from the introduction of its £100,000 experiment in residential areas between The Meadows and Blackford Hill.
Transport convener Lesley Hinds said: “In the pilot area, the level of support for the 20mph speed limit has increased, and was viewed by residents as safer for children walking about the area and to play in the street, better conditions for walking and fewer traffic incidents.
“The speed surveys have demonstrated the 20mph speed limit has resulted in an overall positive drop in speeds.
“Taking account of the positive feedback from this pilot scheme, subject to final approval of the local transport strategy in January, a programme will be implemented to extend 20mph limits to all residential streets, shopping areas and main roads with large numbers of pedestrians.”
Campaign group 20’s Plenty for Us said The Department for Transport (DfT) had recently updated guidance to make 20mph limits in England even easier and cheaper and it expected Edinburgh’s successful trial would help speed up the establishment of similar zones elsewhere.
Director Rod King said: “Twenty mph limits are much in favour with local authorities in England. With the large Edinburgh 20mph pilot coming to an end soon and with its positive results, we expect the Scottish Government to update its 2001 guidance to enable the same widespread use in Scotland’s communities as well.”
Scottish Government-funded umbrella body Cycling Scotland said cutting speeds was key to making communities “more focused on people” than cars.
Chief executive Ian Aitken said: “We’re very much in favour of 20mph zones and area-wide 20mph limits, as they can have a positive impact on traffic speeds and casualties, which helps protect people travelling by bike or on foot.”
However, motoring groups urged caution. Neil Greig, the Scotland-based policy and research director of the Institute of Advanced Motorists, said: “In the right places, 20mph zones are very popular, but their impact on road safety in pure injury numbers is often oversold.
“Projects from elsewhere in the UK have shown mixed results, with speeds coming down but crash numbers much the same and even a decrease in walking and cycling in cities such as Portsmouth.
“If the schemes in Edinburgh have been popular and left residents feeling safer and more likely to cycle, then we have no problem with them being extended.
“However, we do have concerns about blanket approaches, particularly when main roads are included.”
The Scottish Government’s Transport Scotland agency said its cycling action plan included a commitment to promote 20mph schemes in all residential areas.
A spokeswoman said: “Transport Scotland is committed to encouraging local authorities to consider 20mph zones in all residential areas.
“The Scottish Government has encouraged the use of 20mph speed limits in residential areas and around schools, and has issued guidance most recently in 2006.
“Transport Scotland is assisting the City of Edinburgh Council with the evaluation of its 20mph speed limit pilot scheme in south central Edinburgh, which has designated all side streets, and some of the main routes, in the area as 20mph.
“We are aware of the DfT guidance issued in January which actively encourages local authorities to introduce more 20mph limits. When we receive the council’s pilot project final report we will review this, and consider issuing best practice guidance to local authorities.”