The number of serious accidents on 20mph roads increased by 26% last year, according to analysis of Government data by the Institute of Advanced Motorists (IAM).
The IAM says that the number slight accidents on 20mph roads also increased by 17%.
The figures prompted the IAM chief executive to call for the Government to “take stock on the effectiveness of 20mph signs”.
However, Rod King from 20’s Plenty called the IAM “naïve” for “not taking into account the huge increase in the number and length of 20mph streets and roads”.
The IAM says that in the same period, there was a decrease in the number of serious and slight accidents on 30mph and 40 mph roads. The number of serious accidents fell by 9% on 30mph roads and 7% on 40 mph roads, and slight accidents fell by 5% and 3% respectively.
Serious casualties in 20mph zones also increased by 29% while slight casualties went up by 19%.
Simon Best, IAM chief executive, said: “The Government and councils need to take stock on the effectiveness of 20mph signs.
“Recent advice, guidance and relaxation of regulations has all been about making it easier for councils to put 20mph limits in place.
“More and more roads are being given a 20mph limit but they do not seem to be delivering fewer casualties.
“The IAM is concerned that this is because simply putting a sign on a road that still looks like a 30mph zone does not change driver behaviour.
“More evaluation and research is needed into the real world performance of 20mph limits to ensure limited funds are being well spent.”
In response, Rod King MBE, founder and campaign director of 20’s Plenty, said: “We are disappointed that a motoring organisation that claims to be a leading road safety charity should be so naïve as to think that an increase in the number of casualties on 20mph roads is indicative of any sort of increase in danger, without taking into account the huge increase in the number and length of 20mph streets and roads.
“In 2012 some gullible organisations made the same claim and it was investigated by the BBC “More or Less” programme which concluded that the large increase in the number of 20mph roads and consequent reduction in 30mph roads would be expected to account for any such change.
“As the DfT holds no record of the changing total length of 20mph and 30mph roads in the UK then no adverse safety trend can be assumed from this increase.
“There is also public health consensus that 20mph is safer than 30mph. Physics proves it. In the distance a 20mph car takes to stop, a 30mph car is still doing 24mph.”