Rishi Sunak is set to curb English councils from introducing new 20mph speed limits.

The prime minister is reportedly planning to limit the power of local authorities to impose new 20mph zones, restrict the number of hours a day cars are banned from bus lanes, and scale back low-traffic neighbourhoods (LTNs).

Mr Sunak is expected to unveil the new measure as part of a Plan for Motorists at the Tory conference in Manchester, according to several newspapers.

The default speed limit was recently changed from 30mph to 20mph across Wales, making it the first UK nation to introduce a default limit on speed. However, the decision is set to be debated after sparking criticism from a large number of Wales residents. A petition opposing the new 20mph default speed limit in Wales has had a record-breaking number of signatures.

More than 430,000 people have signed it, asking the Welsh Government to “rescind and remove the disastrous 20mph law”.

It beats the previous record of 67,000 set for a Senedd petition about supermarkets being able to sell non-essential items during the Covid-19 lockdown. As more than 10,000 people have signed the petition, it will now be sent to the Senedd’s Petitions Committee to be considered for debate by members of the Senedd.

Politicians have lined up to back the move, saying it would save lives. Mark Drakeford, First Minister of Wales, said the decision had twice been approved by the Senedd and despite the record-breaking petition, he would not be scrapping the policy.

He said that cutting the speed limit would protect lives and save the NHS in Wales £92 million a year, adding that predictions state the change will save up to 100 lives and 20,000 casualties in the first decade.

Mr Drakeford explained: “That is why this Government will stick fast to the decision that we have made, endorsed twice on the floor of the Senedd, not by a simple majority, but by a super majority, because of the human stories that lie behind the decision we have made and will go on implementing here in Wales.”

Similarly, recent years have seen the speed limit on more than half of London’s roads get reduced to 20 mph. According to Will Norman, the capital’s walking and cycling commissioner, Government surveys have found 78 per cent support for 20 mph limits.

Here is a comprehensive look at why these speed limits are being implemented, which areas they impact, and whether they are effective.

Why are 20mph speed limits being implemented?

Following their recent 20mph default speed implementation on September 17, the Welsh Government said the change will save lives and help to build “safer communities” by decreasing the number of car accidents.

It is also expected to make streets quieter by reducing noise pollution, and give people more confidence to walk or cycle around their neighbourhoods.

Similarly, London’s walking and cycling commissioner Will Norman has commented on the 20mph speed limit in parts of the capital, saying: “This helps save lives.”

“For pedestrians just crossing the road, we have seen falls of up to 60 per cent of people hit while they are walking,” he told LBC.

“This makes the city safer for absolutely everyone — not just people walking or people cycling, but people in the cars themselves.”

Where are 20mph speed limits being used in England?

Apart from Wales’s nationwide speed limit roll-out, areas of England have been introducing default speed limits, too.

The UK’s first 20mph zone was introduced in Tinsley, Sheffield back in 1991. Now many UK counties, towns, and cities have adopted 20mph limits on some of their residential roads.

London’s roads within the congestion zone already have a 20mph speed limit, for instance.

Moreover, 11 of the capital’s 33 boroughs have limited all local roads to 20mph — Camden, City of London, Hackney, Islington, Kensington and Chelsea, Lambeth, Lewisham, Richmond, Southwark, Tower Hamlets and Westminster.

Plus, TfL is giving outer London boroughs £2.45 million this year to introduce more 20mph roads.

Where are the 20mph speed limits coming?

The Scottish government is hoping to lower the limit to 20mph in most of its residential roads by 2025.

The plans, devised by the SNP and the Greens, were published as a part of the shares policy programme back in 2021.

As for England, while there have been no nationwide roll-outs, several areas such as Bristol and Manchester have introduced a default limit of 20 mph or have shared plans to do so in the coming times.

While road safety group Brake has called for the 20mph default limit to be extended to England, the UK government has ruled that out.

Are 20mph limits effective?

Speeding is the biggest cause of road deaths. The police reported that in 48 out of the 99 fatal collisions in London last year, speed was a contributory factor.

TfL said lowering speeds was a “crucial part” of its Vision Zero approach to eradicating road deaths. It says that every year, 1,000 people are injured or killed by drivers exceeding the speed limit.

Back in 2021, Spain introduced a default speed limit of 30km/h (18.6 mph) on its roads with a single lane in each direction.

The nation’s directorate-general for traffic later revealed that the move has reduced the risk of death in a road traffic accident. Compared to a vehicle travelling 50 km/h, the risk of death when hit by a vehicle travelling 30km/h was 80 per cent lower.