Dear Umbra,
What is the most eco-friendly driveway material?
Jean K.
Newington, Conn.
Dearest Jean,
Other than "no driveway because no car," dunno. I can tell you all the characteristics possessed by a good eco-friendly driveway material, but no single material pulled ahead of the rest and parked itself in first place. Since I don't know what type of drive you have -- a long and winding road? A mere blip? -- a face-saving answer would be "it depends." But I get a little tired of writing "it depends" all the time. Better to admit out-and-out ignorance sometimes, don't you think?
Not just for cars.
Still and all, I have a few concrete suggestions, and some non-cement ones, too. The constructed driveway protects our land from the depredations of our car(s). When we don't have a designated path -- one that stands up well under duress -- the weight and scouring tires of our giant vehicles wear down the landscape and reduce it to a mud trench. Asphalt-y driveways are certainly durable, fighting off rain and oozing car fluids year after year. The trouble is, in wet weather, the fluids run off the driveway (an impermeable surface), and on sunny days the asphalt becomes incredibly hot (a "heat island"). The runoff damages the land and presents a water management problem in both urban and rural settings. The heat island effect, multiplied by the countless paved surfaces around us, raises local and regional temperatures and creates air pollution and health problems; it also bumps up greenhouse-gas emissions, particularly in urban areas (heat archipelagos, as it were), where soaring temps create soaring energy consumption for air conditioning.
A good driveway material, then, is permeable and not a heat sink. Grass, other tough plants, or dirt are obvious candidates, but they don't meet the durability requirement, so most green driveways combine natural elements with a hard material. A traditional and effective option is gravel, particularly the angular-cut variety, which will hold on to its pebbly neighbor while leaving plenty of space for water to burble through it and into the ground.
At this point, I'm sure some readers are thinking, "There's no way I could have a gravel driveway!" Don't despair: There's more than one route to an earth-friendlier driveway. The Environmental Protection Agency and municipalities in Vancouver, B.C. offer tidy roundups of green pavement options -- some of which end up looking like lawns. These include lattice-like concrete pavers and plastic honeycomb-shaped grid systems, which are laid on a sturdy base such as gravel or crushed stone. Openings in the pavers are filled with soil or sand, and planted with grass. The plastic grid systems [PDF] I came across are made of recycled high density polyethylene.
Some folks are achieving a similar grassy effect with traditional brick or stone, leaving sand-filled gaps between each piece and allowing plants to grow (or not) as they wish. Other options include permeable paving stones and bricks, made from special concrete mixes that allow water to pass through. (Note, however, that cement is an ingredient in concrete, and since cement is made in giant kilns that emit toxic mercury, avoiding concrete when possible is always a good idea.)
Every new driveway material, not surprisingly, brings new ecological considerations. Is the material reclaimed or recycled, and will you be able to reclaim it, in turn, when it needs replacement? What maintenance is required? Is the supplier giving any manufacturing information to help you measure the product's impacts? When it comes to "cool pavement" options or things like pervious concrete, what are the manufacturers claiming in terms of reduced greenhouse emissions? Sadly, I think some of these questions are outside the scope and space I have here. The best choice for you depends on your climate, the size and slope of your driveway, and also (likely) your budget. (Gravel is cheap; permeable paving stones are not.) Go forth and find an expert, and pave your own way in this exciting new field of green.
Punnily,
Umbra
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Comments
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rufwork Posted 1:39 am
01 Oct 2008
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loraz Posted 4:38 am
01 Oct 2008
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rivergal Posted 7:11 am
01 Oct 2008
Plastic grid usually has to be anchored and/or ballasted to hold it in place, using gravel in the cells. It has the advantage of keeping the gravel in one place, too, but I don't think it's suitable for driveways with much slope. Anywhere there's frost heaving masonery and concrete can cause problems -- that's why flexible asphalt is so popular up north.
Porous pavement is perfect for most parking areas but may need to be vacuumed -- using a special machine -- to keep fine particles from clogging the pores over time, especially if you use sand on your drive or if your car picks up a lot of sand and grime from street applications.
Whatever you do, just don't get a heated drive! You'd be suprised how popular they are here (well, given what you all are finding out about our Guv, maybe not . . .) and I cringe every time I see steam rising from one of them.
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katmainomad Posted 9:48 am
01 Oct 2008
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racc Posted 4:16 am
02 Oct 2008
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PolluteLessDotCom Posted 6:43 am
02 Oct 2008
Anyhow, shorter and more narrow drive ways cost less, and require less material, less maintenance, and most importantly, less snow removal. Of course with a shorter driveway also come shorter power and phone lines, shorter water lines, shorter waste water lines, etc. In some areas a shorter driveway removes the need for a 4-wheel-drive vehicle since you are close enough to a road and not up a hill.
If you are connected to the grid (or network of roads), stay close to it!
My two cents.
Karsten
http://www.polluteless.com
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aieageoff Posted 4:34 am
03 Oct 2008
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2wheeler Posted 6:54 am
05 Oct 2008
The sloping portion of the driveway was gravel with grass growing down the middle. We improved the surface of the sloped driveway by salvaging some old concrete sidewalk chunks broken into angular "gravel" of the appropriate size. We used a sledgehammer and wore appropriate eye protection! The surface provided great traction, durability and water permeability. It was free. Our small cars handled it great.
Here in Ohio my parents have a large gravel driveway at their farm which they maintain by grading the surface with the tractor's grader blade about every 6 months or so. They have no problem keeping it clear of deep snow using the same tractor blade. Their driveway has some weedy plants growing through it, which could either be tolerated or pulled, depending on one's preference.
I agree that permeable pavement is best for watershed protection. There is too much hard surface area (roofs and pavement) in the urbanized area already; the rivers are suffering from the storm runoff surges.
My current home has no driveway-- just an alley from which the garage may be accessed. I love it!
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gooseduckstevens Posted 7:33 am
06 Oct 2008
Pavers are expensive and also become impervious over time...especially tight fitting pavers.
Porous concrete and asphalt are a good option, but require a deep uniform diameter gravel base to act as a reservoir. Also, there aren't many contractors that know how to design and install it properly. You can't just hire Joe Concrete Guy down the street or you'll end up with a very expensive impervious porous concrete driveway. The benefit though is that oil and grease and other nasties biodegrade within the pores. You're looking at least a 50% increase in cost over a traditional concrete driveway and you have to vacuum the fines out of the pores to prevent it from clogging. Check out research done by Bruce K. Ferguson in GA.
Something that has been in use for years is the tire strip concrete driveway. You pour two strips for your tires to ride on and in between and all around is grass or another low growing plant, groundcover, moss, etc. You minimize impervious and adjacent vegetation provides some treatment of runoff. You can do the same with pavers...paver strips.
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