Millions more motorists could soon face reduced speed limits as new research by The Independent suggests that more than a third of local authorities have introduced measures to stop drivers exceeding 20mph on at least some roads, or are planning to do so.

In what is being hailed by campaigners as a "cultural shift", as well as a significant reversal in decades of policy which prioritised motor vehicles over the safety of pedestrians and cyclists, new figures show that dozens of cities and towns across England and Wales have either approved slowdown zones or are now considering introducing them. It is claimed a 10mph cut in the maximum speed limit could lead to a 40 per cent reduction in the number of road casualties, as well as reducing pollution, promoting cycling, walking and local shopping.

Meanwhile, public backing for a blanket 20mph limit in built-up areas has reached more than 60 per cent with support particularly strong among women, younger people and pensioners, a ComRes survey for The Independent found.

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Eight million people are already living under authorities where 20mph limits are in operation such as Liverpool, Bristol, York, Newcastle-upon-Tyne and parts of London. Islington in north London is set to become an entirely 20mph zone by March, with the only roads excluded from the scheme those managed by Transport for London.

Of the 75 local authorities in England and Wales that responded to a survey by this newspaper, 27 said they had introduced or were in the process of considering default 20mph zones, while six were awaiting new guidelines from the Department for Transport.

Twelve councils said they were already operating the system while 39 said they had no plans to do so. Four authorities had undertaken some work in the area but their position was unclear.

Although the majority of 20mph zones already established are self-enforcing, with police claiming they have insufficient resources to implement the lower speed, some councils, including Oxford, are planning to make them legally binding. Thames Valley Police recently said it was prepared to prosecute motorists that seriously breached the limit, while a spokesman for the Association of Chief Police Officers called for zones to include measures – such as speed bumps – that "physically ensure driver compliance".

The pressure group 20's Plenty, which campaigns for the lower speed limit, claims there is growing grassroots momentum for a change. Supporters claim the 10mph reduction could breathe new life into areas where people felt intimidated by fast moving traffic. Rod King, founder 20's Plenty, said communities saw levels of support go up after the lower limit had been implemented. "I think people are no longer trying to justify it only in terms of road safety. "

"This is about making places better places to be. There is recognition of very wide benefits. There is a cultural shift that cars can't blight our communities like they have done in the past. It is not about being anti-car. It is about putting it in context of enhanced communities."

The most recent figures from the DfT show that 24,870 people were either killed or seriously injured on Britain's roads in the year to June 2012 – up 1 per cent of the previous 12 months. And while deaths and serious injuries rose year on year by 5 per cent for pedestrians and 9 per cent for pedal cyclists, the number of motorists injured or killed fell by 5 per cent.

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A 2009 study by the London School of Hygiene and Tropical Medicine suggested 20mph limits could reduce casualties by up to 40 per cent. At 20mph only one in 40 pedestrians is killed in a crash.

Lower driving limits have already received the backing of the European Parliament, while the Government said it was up to local authorities to decide whether they wanted them. Local Transport minister Norman Baker said the Coalition had recently consulted on the issue.

"We believe 20mph speed limits are useful in certain areas and support their introduction where it can be shown that they improve road safety and quality of life. However, this is a decision that should be taken locally by councils who know the needs of their area, not in Westminster," said Mr Baker.

Meanwhile, the Government appears to be backing away from its 2011 pledge to raise the motorway speed limit to 80mph after facing anger from road safety campaigners. Although the idea has not been officially dropped inside Whitehall, Transport Secretary Patrick McLoughlin said last month, it was no longer a priority.

According to The Independent poll, asked whether such a blanket limit should be implemented in residential areas to improve road safety, 62 per cent agreed, 36 per cent disagreed and 2 per cent replied "don't know".

Andrew Howard, head of road safety at the AA, said while there was considerable support for the lower limit in theory, disagreements became apparent when defining what areas should be included in the zone. "We very much support 20mph limits on residential streets. The question is what is a residential street? Some roads are used for getting around town and they should remain at 30mph," he said.

Why so slow? the rise of the 20mph limit

One of the key figures in the rise of 20mph speed limits in the United Kingdom is Ben Hamilton-Baillie, an architect, urban planner and traffic consultant whose work and research was influential in moves such as the one by Islington Council in October to limit all of its managed roads to 20mph. Islington claims a 65 per cent fall in accidents in its 20mph areas.

As part of research into how pedestrians and cars can share outdoor space more safely, Mr Hamilton-Baillie spoke to cranial pathologists who showed him statistics proving that the risk of mortality from a car collision isn't just linear – it accelerates significantly after 20mph.

The explanation is that the human skull has evolved to withstand impacts up to around 20mph because that's about as fast as a human can run into something. It's also easier to keep traffic flowing at 20mph as a road with a 40mph limit will need extensive safety controls.