10

In my experience driving through the rain at speeds above 100 km/h results in a cloud of sprayed water behind the car, like so:

splash

However, I encounter more and more recently repaired road sections where the pavement is virtually immune to splashing:

nosplash

Those pictures are taken 10 seconds apart, on the autobahn A5 near Rastatt. I also have a corresponding video, where the exact border between old & new pavement can be seen.

Can anyone explain how new pavements achieve this remarkable performance at eliminating splashing?

What properties help draining water so effectively?

  • Possibly when they laid the new tarmac they cambered the road so the water runs off to one side? – ceefax12 Jan 12 '16 at 22:38
  • @ceefax12 I don't think so. Even a moderate camber angle wouldn't help in heavy rain like this. Also, I didn't notice any water running to the sides in picture #2, the pavement was just moist. It almost looked like it had pores to drain water through. – Dmitry Grigoryev Jan 12 '16 at 22:57
  • 1
    While this is an interesting question (and I think I know the answer), how does this have anything to do with Motor Vehicle Maintenance and Repair? – Pᴀᴜʟsᴛᴇʀ2 Jan 12 '16 at 23:08
  • @Paulster2 It doesn't, this site simply seemed like the best fit. Also, similar questions (advice on driving on snow, adjusting mirrors etc.) which have nothing to do with maintenance seem to be happily answered here. – Dmitry Grigoryev Jan 13 '16 at 7:30
6

Although I am unsure of the material that is being used for the roadway in your photos it appears similar to Topmix Permeable concrete

You asked

Can anyone explain how new pavements achieve this remarkable performance at eliminating splashing?

Response

Topmix Permeable concrete is simply a very porous concrete interlaced with large rounded pebbles. In order to allow as much water as possible through the roadway and continue to absorb liquid a base of rubble and channels must be formed. They do not eliminate splashing so much as they absorb and allow liquid to drain down through the surface.

enter image description here

enter image description here

Other Technology

The State of California in the US has an initiative of porous concrete solution combined with recycled rubber from tires. Here is a state government technology guide describing the initiative and the technology.

Cost Justification

Drivers of cars can allow their tires to become degraded and wait until the last minute to change them creating a safety issue due to bald tires and what not. The cost to the government for the healthcare of these individuals can be relatively high. A proactive cost control method employed by the state could be to employ this type of road technology to decrease the number of accidents annually. The one time cost of implementation could be less than the cost related to the healthcare of individuals who suffer crash related injuries in the rain.

  • 1
    Actually, it's asphalt in this case. – sweber Jan 13 '16 at 10:31
5

It's Flüsterasphalt

(literaly whisper asphalt)

@DucatiKiller has already given a nice answer about a concrete version of this, however, this is really asphalt and is also processed more or less like standard asphalt (Lots of heat etc.).

The one and only reason why this is used here in Germany is to reduce the noise of the wheels on the road, and it really makes a big difference, even on a dry road. It seems there's no noise from the wheels any more.

Cars make even more noise on a road with water on it, but this is completely swallowed, too.

Of course, having no water on the road is safer, too: Better visibility (see your pics) and more grip.

That point of @DucatiKillers answer about cars with worn tires was never discussed here.

The draw back of Flüsterasphalt is that the pores will clog up over time with dirt and rubbed-off material from the wheels, so the noise reduction effect doesn't last very long. Another point is that water enters the asphalt and can break it up when it freezes.
It's said that Flüsterasphalt lasts for about 8 years, while standard asphalt lasts up to 20 years.

Near cologne, they used this asphalt a couple of years ago, but next year, they already have to exchange it...

Ah, and by the way: Some cities like mine now start to use it on big roads in the center of the city. But at the low speed limit there, noise of the wheel usually isn't an issue...

  • Now when I think about it, this section does seem to be more quiet to drive on, even when dry. Also supporting your opinion on worn tires: if anything, having such roads everywhere (e.g on 90% of roads) can only encourage people to keep worn tires longer, making the remaining 10% of the roads more deadly. – Dmitry Grigoryev Jan 13 '16 at 10:37
  • @DmitryGrigoryev I very much doubt that people who wear their tyres until bald are doing a risk/cost analysis. I fact I doubt they think about their tyres at all, so they're unlikely to wear them more. – Chris H Jan 13 '16 at 11:30
  • @ChrisH But it would concentrate their catastrophic failures (which would happen at the same global rate) in the 10% of roads that have a conventional surface. – Random832 Jan 13 '16 at 15:17
  • We have currently less than 100 out of 13000km autobahn with this asphalt. So it's actually not that much. Also, cars need to have at least 1.6mm tread left. While that's not much, it's checked every 2 years. (Fines range from 60 to 120€, not that much, too...) – sweber Jan 13 '16 at 15:24
1

I cannot know for sure, but the new pavement may be more permeable than the old, allowing water to quickly drain directly through the roadway, rather than collecting on the surface and having to run off the sides.

See this video for a demonstration

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.