Why is new tarmac quieter than old tarmac?

[Paul O]

Anyone know?

you can really tell the difference when they re-lay roads (and I don't mean that crap glue-and-scatter method, but propper tarmac).

When they repair parts of the road, you can hear a notable difference as you bump onto the new bit and off onto the old bit.

Whats that about?

[mike-r]

Softer?

[BGarside]

Smaller contact area with the tyres, as the chippings are 'pointier' having not been worn?

Just a guess.

Also some tarmac is special low-noise type - typically laid around residential areas. Cycled over some in York recently and passing cars are much quieter.

[Conscript]

Not all asphalt is the same. Different companies make different grades and qualities of asphalt. Which one gets down depends on the specification and requirement of the road it's being applied to.

Noise can be affected the hardness of the asphalt and the size/amount of aggregate it contains. Typically, asphalts which provide less road noise are also likely to not be as hard wearing. So whilst it may be suitable for a road in a residential area, it wouldn't be as cost effective on a motorway, where your more likely to see a much harder (but noisier) blend of asphalt used.

[Vlad the Imp]

Conscript said:

Noise can be affected the hardness of the asphalt and the size/amount of aggregate it contains. Typically, asphalts which provide less road noise are also likely to not be as hard wearing. So whilst it may be suitable for a road in a residential area, it wouldn't be as cost effective on a motorway, where your more likely to see a much harder (but noisier) blend of asphalt used.

Unfortunately the above is what is known technically as complete bks, hardness of the asphalt or how hard wearing it might be has got bugger all to do with noise. Older asphalt surfaces particularly on motorways consist of a flat surface into which aggregate chippings are rolled. These chippings can be thought of as standing proud of the surface and move the tyre tread blocks more, generating more noise. More modern surface courses, known generically as thin surface course materials are essentially a flat surface with holes in it. This generates less block movement and also to some extent reduces sound wave reflection from the surface.

Suppliers have a range of different thin surface course systems which can be used to achieve varying levels of perceived noise depending on the site. In fact low noise surfacings are most likely to be used on motorways where high traffic speeds mean that vehicle noise is dominated by road/tyre interface noise, rather than at low speed where engine noise dominates.

[Conscript]

I was taught wrongly then and stand corrected.

Thanks for the polite clarification.

Edited by Conscript on Thursday 1st May 18:48

[lazy_b]

Vlad the Imp said:

Unfortunately the above is what is known technically as complete bks, hardness of the asphalt or how hard wearing it might be has got bugger all to do with noise. Older asphalt surfaces particularly on motorways consist of a flat surface into which aggregate chippings are rolled. These chippings can be thought of as standing proud of the surface and move the tyre tread blocks more, generating more noise. More modern surface courses, known generically as thin surface course materials are essentially a flat surface with holes in it. This generates less block movement and also to some extent reduces sound wave reflection from the surface.

Suppliers have a range of different thin surface course systems which can be used to achieve varying levels of perceived noise depending on the site. In fact low noise surfacings are most likely to be used on motorways where high traffic speeds mean that vehicle noise is dominated by road/tyre interface noise, rather than at low speed where engine noise dominates.

Is that why the "low spray" motorway surfaces (I'm thinking of the M4 around Cardiff) always sound a lot quieter than regular surfaces?

And let's not get into describing the hideously noisy grooved concrete A4232 into Cardiff past St Fagan's...

[Vlad the Imp]

I'm not sure what the surface on the M4 at Cardiff is, if it's a more modern thin surface course it will have spray reduction characteristics as well as being quieter. It may be porous asphalt which is similar but has more holes or voids in it allowing water to drain through the surface to an impervious layer underneath. The additional voids give better noise absorption characteristics making for a very quiet surface.

[Sandcrook]

As far as I am aware there are different types of tarmac .The quiet on is called open textured and the water drains through it and therefore causes less noise pollution and the normal tarmac is dense which is just noisy . As far as I was aware the Government were supposed to replace the tarmac on motorways with the quiet type as an ongoing thing but as usual they have run out of money so its back to the high noise one .

[Sandcrook]

I also forgot to say that the open textured quiet tarmac does not last more than ten years and is considerably more expensive so it might be obvious why the Government dont use it .

[MatrixXXx]

what about concrete roads? I was told they were designed to be noisy to stop people driving fast?, abroad they use concrete but the lines are in the direction of travel and quiet.

[Vlad the Imp]

Concrete roads are noisy for a variety of reasons: The have a brush finish perpendicular to the direction of travel to give skid resistance, the nature of concrete means it reflects sound waves very well and usually have joints every 5m which generate more noise.

Experiments have been done to grove concrete in the direction of travel and this does reduce tyre noise. However the skid resistance falls quite quickly and the UK has one of the most demanding requirements for skid resistance of its roads.

Guess what I do for a living??