Many crashes could be caused by a roads surfacing material that's being misused, according to police crash investigators. They're worried because in certain conditions, stone mastic asphalt (SMA) offers little grip for two years until bedded in. And SMA is the blacktop often used for motorways and main roads in the UK -- yet it's been banned in Ireland because of safety concerns.
On BBC Radio's File on 4, police sergeant Jim Allen reported how in 2001 he tested some newly laid SMA on a warm sunny August day, in the course of investigating the cause of a crash. He said, "I jumped on the brakes and the car just kept going and going. Instead of the screaming of tyre on road and a cloud of smoke, there was just a gentle hiss and I skidded far further than I ever expected to."
He said that he was very surprised and concluded that the grip level was low. Investigating further and examining the tyres of his car, Allen found that the heat generated by the tyres as they braked had melted the bitumen so that, instead of gripping stones, the car was floating on molten bitumen.
File on 4 highlighted how resistance tests are often carried out in the wet and on worn surfaces but not in dry conditions, which is just when SMA's critics say slipperiness occurs on new, dry roads.
One local council carried out tests and admitted there were problems. Yet an industry body said that it didn't test for skid resistance on new roads because it assumed older roads would cause the problem.
Eire has now banned SMA from roads whose speed limit is above 30mph, and has resurfaced SMA-laid faster roads. Germany, the pioneer of SMA use in the 1960s, has also seen concerns about grip, as has the Netherlands.
The UK's Highways Agency said that British SMA in Britain has a different consistency, and that the materials have been thoroughly inspected. And File on 4 reported that SMA is the only surface that is approved for unrestricted use on the UK's roads of all types.
The AA Motoring Trust warns the road network is in its worst condition since the 70s and said: "Surfaces are a hidden menace. In London as many as a third of main roads need looking at. There could be lives at risk."
The Government says it is spending more than £31 billion over 10 years on highway repairs.