It's raining, it's pouring,

the roads are getting flooded. Oh wait that's not how the song goes. I've mentioned heating elements for roads when the ice appears, but oh what to do with the run-off. Our drains couldn't cope with the snow, heck watching now they can't cope with rain. This is something I've noted since I started driving oo way back when and over the years to friends I occasionally popped up with a "Why aren't roads porous?" This would normally be after someone's complained that they've got drenched by a passing car, or that it was almost impossible to see due to the glare on the road. It came up again discussing the water boards ineffectiveness towards all that water that falls from the sky

"Over the last year, much of the rain that has fallen has made the surface wet then either run off where the rain has been particularly heavy, or evaporated."

this from an official spokesman during the drought and hosepipe bans.

Well for various reasons I've been prompted to have a look into it. Googling porous roads comes up with several results in Singapore and a link in the UK yay that mentions SUDS wow it even states

"Traditional drainage practice is designed to move rainwater as rapidly as possible from the point at which it has fallen to a discharge point, either a watercourse or soakaway. This approach has a number of adverse impacts:"

Been saying that for years.

So why didn't SUDS appear in my search. Foolish me I searched for porous roads and I should have searched for permeable surfaces. That hopefully would have led me to CITA page on Permeable surfaces and filter drains Things are looking up

Porous paving blocks with a system of voids within the unit [and]
Continuous surfaces with an inherent system of voids

Sounds like roads to me. So seeing as we've got 375,000km of road in the UK and assuming an average width of 7m makes 2,625km². That's an area larger then Greater London all discharging its water straight into the sewers or letting it evaporate. Presumably the Highways Department are making a big deal of this. Well they've got a whole section on "Respecting the Environment" in their Knowledge Centre. Headings are

• Noise
• Air Quality
• Litter
• Ragwort

But wait under "Other" we have Building Better Roads: Towards Sustainable Construction, 2003 Hmm four years old, but still

• Introduction
• Management of Natural Resources
• Reducing Emissions
• Reducing Energy Consumption
• Biodiversity
• Landscape Townscape and Heritage
• Respect for People
• Partnerships to Better Business
• Tools

Nope the only comment about water is about using more in construction (as it's reusable) and about pollution from run-off.

Okay how about using their search box "permeable surface" produces 7 results. Bridges; bridges; oo

"They include that the material should be highly permeable"

Ah no that's any waste from a road building project; limestone; existing soil; problems with spillage; existing surface again. Maybe I'm looking under the wrong search term?

Porous surfaces leads to "Porous Asphalt" Yep this is the stuff I want. The gist is it was recommended to be used "where appropriate" in 1994. So is it being used anywhere? Good old Google

"Since 1993 porous asphalt has been specified in various construction and maintenance contracts, but the tender values received have been higher than expected. The relatively high cost of porous asphalt in comparison with other wearing course materials has been a deterrent to its use, particularly when its justification is primarily aimed at noise suppression. This has lead to porous asphalt only being used where its benefits clearly outweigh the increased initial costs, reduced service life and increased winter maintenance requirements"

So we should use it, but it's a bit expensive so we haven't; well not much. 11km of the M25 in 2000 were doen in porous asphalt; initial costs were £14m, moving up to £34m once they'd actually looked at it properly. The telling phrase is "noise suppression" go through the HA reports and that's what crops up again and again despite one report even stating that porous asphalt reduced spray by "more then 90%". I think HA need to get off the noise-mobile and start looking at the other implications.