Following up on the article "UK experts are giving improper advise on winter tyres":
After five crashes in 12 hours, a curve in Evercreech (Somerset) has been dubbed "Britain's most dangerous bend".
The local Council as well as Fire Rescue Dept are unsure what is causing the crashes.
The answer is quite obvious: Cornering this bend at frequent speed requires more grip than the tire/road contact provides!
The lateral forces acting on a cornering vehicle are controlled by
speed (squared), curvature (1/curveradius), pavement camber and tire/road friction. On bumpy roads also road roughness contributes, but this bend was resurfaced only three years ago so it is likely fairly smooth. This leave Sherlock Holmes with issues on
A) The pavement camber being too small, or even worse, tilted in wrong direction so it adds exciting force instead of reducing the cornering force given by the speed/curvature ratio.
B) The tire/road friction was too low in the chilly winter.
The problem could be A, B or A + B.
"A" is a matter of road design. It can easily be checked by using a mobile road profilometer, operated on behalf of UK Highways Agency for standard pavement condition control. If the curve suffers from adverse camber, it should have its pavement geometry (cross slope AKA superelevation in curve) redesigned and reconstructed ASAP.
"B" is a matter of both pavement macrotexture (0.5 to 50 mm "waves") and of winter tire properties. In case of a slick road surface, it can be retextured by special machines available in the UK. Retexturing can be made by methods such as bush hammering, water jet cutting or steel ball blasting. The result is in either way a macrotextured surface with good wet friction.
A larger problem in the UK is louse winter tyre properties. In the Nordic countries, all car owners change to special tires with larger grooves and made by rubber compounds that stay soft and give good road grip also at temperatures below 7 deg C (45 deg F). This is in strong contrast to over 97 % of UK car owners driving on tires that are unsafe at temperatures below 7 Deg Celcius, not to mention unsafe on frosty and icy surfaces. This unsafe practice in the UK is much due to improper advice on what tire to buy, given by UK traffic "experts". In fact, these experts are totally wrong on what they call "costs for winter tires". The real cost for owning and driving on safe winter tyres are less than 10 % of what the UK experts claim.
In order to reduce UK crashes such as those piling up at the Evercreech bend, three key actions should be taken:
1: Road agencies should use mobile laser/inertial road profilometers to identify adverse cambered bends and reconstruct their crossfall.
2: Road agencies should use mobile laser/inertial road profilometers to identify sections with low macrotexture and hence risk for low wet friction. These slick candidates should then have their wet friction measured by a friction metering device, with at least 0.5 mm water film on the surface during the test. In case of low wet friction, the surface must be retextured. (In Nordic countries, retexturing is done "naturally" by those cars who have studs in their winter tires).
3. UK car owners should buy a set of new or used rims, on which they have real winter tires (studless) mounted. While driving on the winter tires, the summer tires are stored and hence the cost/mile driven is not increased much. With real winter tires, there wouldn't have been five crashes in 12 hrs at the Evercreech bend last week.
It is time to dub 97 % of Britains car tires to "Britains most dangerous tires at winter temperatures"!