Rain-friendly tarmac - Dave H
This might be old hat to people who live south of Preston but last week on a journey from Cumbria to London, I drove through some heavy rain on the M6 and M1.

I was very surprised to find that on newer stretches motorway, the road surface seemed to 'soak up' the spray to the extent that it was like driving in dry conditions, other than the rain hitting the windscreen. i.e. there was no spray at all from the wheels of other vehicles.

I am very curious as to how this works. Can anyone shed any light?


Re: Rain-friendly tarmac - Dwight Van-Driver

Is this the fairly newly surfaced section? If so then they may have increased the camber angle to allow quicker drainage to the soakaways at the side.
Re: Rain-friendly tarmac - John
A lot of research has been done on open textured, porous, surfaces. This is now being used on new surfacing in Kent. The water is allowed to partially penetrate between the granite stone top surface and runs off to the channels beyond the hard shoulder or in the central reservation. Most Motorways have, up to recently, been surfaced with Hot Rolled Ashphalt and Chippings ( to improve wear and grip)or Concrete. Both surfaces retain the water on the surface whilst it runs off. Therefore the new type of Mastic asphalt open textured surfaces allows the water to run off within the surfacing material.
Im not technically involved in the production of this new material, but hope it may help.
Re: Rain-friendly tarmac - andy bairsto
German concrete autobahns are built in the same way with i rippled surface which allows the rain to run of into the soakways.The water then goes into gravel lined lakes with reeds and this takes the impurities out of the water before releasing it into the wild,a bit like a septic tank.
Re: Rain-friendly tarmac - Stuart B
The new open texture tarmac not only helps with rain/spray but also noise and improves grip apparently. I have heard it is not so hard wearing though.
Re: Rain-friendly tarmac - John Regin
The A31 Bentley by-pass (Hants) had one of these surfaces, brilliant when it rains, absolutely lethal on those occasions (admittedly rare these days) when it freezes. Police usually have to close the road.

Re: Rain-friendly tarmac - Andrew Moorey (Tune-Up Ltd.)
We have it on a short stretch of the A24 round Southwater in Sussex. It has reduced road noise by at least 75% and there is little standing water even in torrential rain.
Re: Rain-friendly tarmac - Michael Thomas
The M40 is covered in this pretty much all the way to J1 Uxbridge to J18+ to Brum. Compared the to A40, its amazing to go from lots of spray to none at all.
Re: Rain-friendly tarmac - Rebecca
I think a stretch of the Newbury bypass had this (A34), but within a year the surface was badly damaged/worn and had to be replaced. I don't know what with.
Re: Rain-friendly tarmac - Brian
Re: John Regin's comment:
You can get the same lethal effect on the anti-skid surface dressings used coming up to traffic lights and crossings.
If you have rain and it then freezes, the water retained between the fine chippings on the surface turns into an ice rink.
I have come off a motorcycle trying to brake on this type of surface in those conditions, when the non-treated surface was perfectly rideable.
Re: Rain-friendly tarmac - Andrew Hamilton
Problem is it costs more to put down than normal tarmac so will not be widely done.
Re: Rain-friendly tarmac - John
Brian. I don't doubt that you will still have the danger in freezing weather but when above freezing it clears water more quickly.
Andrew. Sorry but I take issue over the cost. It is cheaper because it involves only the resources to lay a single wearing course and not in the case of hot rolled asphalt, as second crew to lay and roll pre coated chippings into the surface.

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