The new limits – which were cut from 30mph – will be enforced across all 8.9km of Transport for London’s roads within the capital’s Congestion Charging Zone, including Victoria and Albert Embankments, Millbank, Tower Hill, Blackfriars Road and Borough High Street.

The move is supported by new signage and road markings, while raised pedestrian crossings are also being installed in locations of high footfall such as near Embankment and Tower Hill underground stations.

“Millions of walking and cycling journeys are made across our city every single day and a person is five times less likely to be fatally injured if hit at 20mph than at 30mph,” said TfL’s chief health, safety and environment officer Lilli Matson.

“'It’s clear the new 20mph speed limits will not only save lives but will also encourage Londoners to travel in more active and sustainable ways.”

Road safety campaigners and sustainable travel champions have welcomed the move, which it is hoped will reduce the number of people killed or seriously injured in speed related collisions. These incidents cause approximately 130 deaths per year on the capital’s streets.

Safety charity RoadPeace’s campaign coordinator Victoria Lebrec said: “We see the devastation that speed causes every day, and the few seconds that are saved can lead to a lifetime of misery for a victim.”

She added: “While TfL's plans are encouraging, they represent a small percentage of the roads in London. We would like to see more boroughs adopting a 20mph default speed limit.”

London coordinator for campaign group 20’s Plenty Jeremy Leach said: “Getting maximum speeds down to 20mph has a huge impact on making roads feel and be safe for all Londoners.

“We look forward to news of more 20mph limits on TfL's Red Route roads and more encouragement for the last few London boroughs to go 20.”

Cycling group Sustrans’ England director Matt Winfield agreed that lowering traffic speed can help make streets feel safer. “Studies have shown that slower roads lead to more people choosing to walk, wheel and cycle their everyday journeys so there is huge potential that, with lower traffic speeds and less car dominance, we will see a healthier, happier London for everyone.”

However some have questioned whether the new speed limits will make a difference, with average speed limits across central London currently standing at just over 7mph between 7am and 7pm.

RAC head of roads policy Nicholas Lyes said: “TfL’s new speed limits put safety at the heart of the changes, but the reality for drivers is that average speeds are now so low on central London’s roads that many drivers are unlikely to reach such speeds during busy periods.”

Freight Transport Association’s urban policy manager Denise Beedell said: “While 20mph speed limits have a useful part to play in increasing road safety – for example, in accident black spots or around sensitive locations such as schools – they should not be applied in a simplistic or blanket fashion.
 
“We fear that by making the 20mph rule apply throughout central London, it will reduce private drivers’ willingness to obey the speed limit anywhere, particularly in safety hotspots.”

Transport for London says it will work with boroughs to introduce 20mph limits more widely across the capital in the next five years. It is also developing proposals to reduce speeds at a number of key high risk areas, including Edgware Road.

(Photograph: Transport for London)