AA Calls For Government Tread Depth Review

The AA Motoring Trust and County Surveyors’ Society (CSS) have called for the government to lead a review of the 1.6 millimetre tread depth limit. The call comes in response to “research evidence from real crashes,” says the groups’ recently published report. At the same time the document called for greater local authority investment in road surface renewal.

With reference to wet road traction, the report stated: “Grip on wet roads is markedly reduced when tread depth is less than three millimetres…when there is a two millimetre film of water on a road, even two millimetres of tread may give no better stopping friction than a bald tyre.”

In addition, the two-year study reported that just one in 20 tyres are inflated correctly, while as many as 17 per cent of main roads fail basic skid resistance tests. Researchers found that 10 per cent of cars have illegal tyres, 90 per cent of tyres are wrongly inflated and up to a half of garage air pumps are inaccurate. In response to this specific point the report urged garages to keep pressure gauges clean, accurate and easy to use or remove them from service.

In order to reduce accidents, the authors recommended that motorists monitor tread particularly carefully after three millimetres and ideally replace tyres soon after the tread reaches this point – “since tyre grip is substantially reduced below this depth.” At the same time the association warned motorists: “Do not buy used (part-worn) tyres.”

Speaking to the tyre industry, the report’s authors recommended that increased industry-funded research on the role of tyre characteristics in real word accidents should be carried out. The message that pairs of new tyres should be fitted to rear rather than front wheels should also be emphasised, said the report.

“The quality of surface maintenance on many roads is not good enough and the minimum threshold for tyre tread depth may no longer be adequate. A review is now needed of the minimum legal tyre tread depth of 1.6 millimetre based on research evidence from crashes,” said Bert Morris, the AA Trust’s director.

Geoff Allister, CSS president commented: “How well rubber and road grip each other can be the difference between life and death in crashes and near misses. We need much greater investment from local authorities in road surface renewal – few other budgets have such an influence on life and death in their communities. It’s time for society to treat road crashes resulting in death or severe injury as seriously as those in the air, on the railways or in the workplace.”