For most pedestrians, the sidewalk is an unnoticed facet of the everyday streetscape, like a telephone pole, traffic signal, or postal box. But the choices made about the materials to use for building and installing sidewalks can significantly affect the atmosphere of an urban environment.
For most American cities, concrete is the go-to choice for building sidewalks. It’s relatively cheap to install — only about $12 per square foot — and it’s very solid. Its pale color reflects light, reducing nighttime illumination costs for cities compared to darker-hued alternatives. Plus, if adequately maintained, concrete can last up to eighty years.
Yet concrete also has its downsides: Manufacturing it has a high carbon footprint, since its fabrication requires the energy-intensive heating of limestone; it has a tendency to crack when tree routes grow underneath it; and it has no porosity, depriving the ground under it of essential ground water and increasing runoff problems.
Most importantly for sidewalk users, though, is the fact that concrete rates poorly from an aesthetic perspective — in other words, the older it gets, the uglier it gets.
As a result, cities around the world have invested in a number of alternatives, to varying success. Asphalt — the stuff usually used for the roadbed — is actually a cheaper option, but it’s seen as too poorly differentiated from the car path, putting pedestrians in danger. It’s also far more susceptible to damage in cold and wet weather.
Brick is a frequent choice in historic neighborhoods, since it gives off the sense of craftsmanship and handiwork. But as a material for the average walker, it’s pretty miserable. It becomes incredibly slippery in the rain or snow and it breaks up easily over time. (That said, a broken brick is far less unsightly than a slab of cracked concrete.)
Other urban areas have invested in stone slabs and cobblestones — materials common in European cities like Paris (as shown in the picture above) — where they’re praised for their attractive looks and solidity. Toronto is currently replacing the sidewalk on one of its major corridors with granite, with the idea that a better looking sidewalk will encourage more people to walk around, and thereby increase area property values.
But heavy stone like granite and marble is expensive to buy. In Beverly Hills, California, installation costs $850 a linear foot – far more than other materials. Some stones can even be a liability, since they become slippery more easily than concrete. And they trip up the movement of people who rely on mobility aids like walkers and wheelchairs, and need more even surfaces.
For now, then, concrete remains the most reliable option — and a relatively cheap one at that. Yet there may be a better future, and it’s made out of rubber. Several companies have developed sidewalk panels recycled from used automobile tires, saving material costs and reducing ecological impact. They have a high amount of porosity, limiting runoff and preventing area flooding.
Per square foot, they’re just a bit more expensive than concrete. and they’ve already been installed in several American cities, including Seattle. Yet, they’re just as sad looking as a common concrete panel, doing nothing to enliven the street.
In the end, there may be nothing better than the textured, high-quality feel of the sidewalk stone so noticeable in European cities. It’s just so darned expensive!
Image above: Paris’ Champs Elysées, from Flickr user Achim H
February 22nd, 2010 at 6:00 pm
I’ve looked into pervious concrete (http://en.wikipedia.org/wiki/Pervious_concrete) in the past, for drainage issues. There was sadly very little information online regarding longevity when I looked a few years ago. I’d love to see this kind of thing become popular for sidewalk material, as melting snow would seep through it rather than forming fun little ice patches (as occurs here in Boston on concrete sidewalks).
February 22nd, 2010 at 6:07 pm
…but think about both the cost relative to what we spend on our road paving materials, as well as the relative longevity… there are cobblestone sidewalks in Europe that are a few hundred years old and still serviceable - even in Portland, we have cement sidewalks that are over 100 years old and still in pretty good shape. Don’t think we can say that of any of our road surfaces
February 22nd, 2010 at 6:33 pm
In some of its older neighborhoods, Denver has some sort of slate-type sidewalk. Does anyone know more about them?
February 22nd, 2010 at 7:01 pm
Several California cities use rubberized sidewalks to accommodate tree roots: Bakersfield http://www.bakersfieldcity.us/cityservices/pubwrks/streetdiv/rubber_sidewalk/index.htm; Stockton http://www.stocktongov.com/publicworks/OandM/rubberSidewalk/index.cfm; and Santa Monica http://www.usatoday.com/news/nation/2006-09-19-sidewalks_x.htm. D.C. does, too: http://www.washingtonpost.com/wp-dyn/content/article/2006/07/01/AR2006070101087.html.
February 22nd, 2010 at 7:38 pm
My guess is that rubber sidewalks could easily be colored with attractive patterns and even original artwork. A city like Seattle could just hire a group of artists to make sidewalk art that connects with the neighborhood.
February 22nd, 2010 at 9:24 pm
Concrete does not have to have such a carbon footprint. Coal fly ash (from power plants) is naturally pozzolanic (self-cementing); available in large quantities; safe and cheap; and, would eliminate the need to cook limestone.
Sure, it comes from burnt coal. However, we do that anyway to produce electricity — so we might as well not use more juice to cook limestone AND use as much as possible form the coal we do burn.
February 22nd, 2010 at 10:46 pm
I understand the need for an alternative to the current materials but I’d keep looking. Rubber is actually dangerous for individuals with latex allergies. I’ve seen people puff up from eating at a restaurant that uses latex gloves. It’s also the type of allergy that develops and worsens with increased exposure. Medical facilities are shifting to vinyl gloves because employees are developing allergies. As far as bricks or cobblestone goes, it’s beyond unsafe. For elderly or disabled individuals who use walkers these kinds of surface increase the frequency of accidents. The baby boomers are aging and while you may be a fit and physical fifty, your walker or oxygen tank is going to be problematic if you intend to be an active seventy or eighty year old. Aside from danger, the cobblestone, brick, etc. is highly annoying for people like me. As a wheelchair user, the aesthetic benefit is overshaddowed by the headache from bobble-heading for a couple blocks. And see how awesome stollers with sleeping babies or those strollers for jogging are on the new terrain. I can’t offer a good solution but I can tell you these alternatives would be highly unsuccessful, at least for some of us.
February 22nd, 2010 at 11:49 pm
It’s interesting to see alternative materials for footpaths being used. I can the benefits of using recycled rubber, being, one, it’s recycled, and two it is porous, however I can also see a few potential negatives, namely, they appear to be square tiles of rubber, so what happens when the underlying ground starts to settle at different rates, or tree roots grow under the path? I’m guessing you’d probably end up with tiles at all different levels resulting in trip hazards for pedestrians. Also how grippy are they during wet weather? From photos the rubber paths in Seatle seem to be fairly smooth. One of the advantages of concrete is that with broom finish the path remains fairly grippy during wet weather.
I’m all for innovation, it’s just that innovators need to fully understand benefits of any existing system, and make sure they are incorporated in to any new system. Otherwise we end up with innovations that are a step forward in one aspect, but introduce a whole bunch of “new” problems, that possibility didn’t occur with the old system. Kind of LED traffic lights. They’re great they use less electricity, but in snowy climates they don’t get hot enough to melt the snow, and the snow makes the lights not visible to motorists.
February 23rd, 2010 at 1:47 am
Rubber sidewalk in Japan…. you don’t have to make it look like concrete….
Is it also really comfy to walk/run on since it has a bit of a bounce/softness to it.
http://www.flickr.com/photos/8622781@N06/2527448071/
February 23rd, 2010 at 8:20 am
As someone who lives in Berlin, I’d just like to say that I long for the normal sidewalks of North America. Much of the original, older sidewalks here are granite slabs and they’re just treacherous. They’re actually more slippery than the ice, and I go out of my way to walk on the ice instead of the granite. Even older are the cobblestone sidewalks, which not only are just as slippery as granite but it’s uneven and tends to roll the ankles at will. Much of the old West Berlin used/uses some sort of manifactured concrete slabs of some sort about 12″ square. This is a better solution, but it tends to heave and crack and it doesn’t look much better than concrete. And don’t even get me started on the mosaic like 2″ granite pieces this city uses.
With the exception of areas around historic buildings and plazas I think concrete is the better solution. For safety, snow removal and longevity.
February 23rd, 2010 at 12:07 pm
Any sidewalk is better than no sidewalk. Not having a sidewalk discourages walking and kids playing. No sidewalk gives a street an empty feeling as well.
February 23rd, 2010 at 12:54 pm
There is a rubber sidewalk in my neighborhood, installed two or three years ago. It has settled and no longer provide a smooth, level walking surface, no longer ADA compliant. It also seems to be degrading quickly. It is NOT comfortable to walk on, due to the rippled or wavy, unpredictable surface.
February 23rd, 2010 at 12:55 pm
There are also surface treatments for concrete that are durable, slip-resistant and create a more attractive product, such as fine, exposed aggregates.
February 23rd, 2010 at 2:40 pm
“Asphalt — the stuff usually used for the roadbed — is actually a cheaper option, but it’s seen as too poorly differentiated from the car path, putting pedestrians in danger.”
Well, not necessarily. The shared streetscapes model seems to indicate that, in the absence of lane marking and curb delimiters, traffic SLOWS. Slower cars are pretty much always going to be safer for pedestrians in terms of serious injuries/fatalities, no matter what.
The fetishization of everything European, and the prioritizing of the aesthetic over the practical in civil design, infuriates me. I don’t care how pretty the stone sidewalks of Europe are: they are slippery and hard to walk on if you have poor vision or limited mobility. Why are we so eager to return to a time when it was extremely difficult for handicapped people to live independently? Let’s find ways to make concrete look better and work better (plasticizing agents? aggregates? thicker, more durable pouring methods?) and stop fantasizing that we will ever be able to employ the kind of manpower needed to return our urban pathways to hand-set cobblestones.
This whole issue is strongly reminiscent of how shopping malls all tore up their serviceable linoleum floors in the late 80s and 90s and laid down marble instead because it is more upscale. Now, elderly people like my mom can’t shop there, because the smallest drop of spilled coffee renders it an ice rink and she can’t risk breaking a hip. Not to mention how awful it is on the joints of the low-wage workers who have to stand on it for 8 hours a day.
February 23rd, 2010 at 7:29 pm
A more important point, Angela— that photo of “common” Paris is in front of the Louis Vuitton store on the Champs-Elysees near the Arc de Triomphe… in other words, pretty much the nicest showcase block in Paris… so yeah, they have nice stone streets THERE.
Walk around the rest of Paris and the sidewalks look pretty much exactly like they do in New York, Chicago, LA, etc.
Fetishization indeed.
February 24th, 2010 at 2:46 am
There are parts of Times Square that look like they use schist for the sidewalk. It looks like sparkling concrete. What’s the carbon footprint of that?
February 24th, 2010 at 3:43 am
We can solve the problem of tree roots with device I once saw. It was nothing more than cylinder and it forced the tree roots to grow down rather in their more organic fashion. I don’t know why it isn’t used. Maybe it kills trees in the long run.
February 24th, 2010 at 5:07 am
The recycled rubber tire paving is very un-enviromentally friendly, lots of metal toxins (lead, etc) in it, and it gets much hotter on summer days than grass (not sure about asphalt vs concrete vs crumb rubber temperature). Tires were never made with the intention of being used for paving and playing surfaces.
http://www.delawareriverkeeper.org/newsresources/factsheet.asp?ID=50
February 24th, 2010 at 1:00 pm
[...] Comparison of materials used in city sidewalks. (Infrastructurist) [...]
February 24th, 2010 at 1:58 pm
Neil, the sidewalks you’re talking about are actually sandstone. Back when Colorado had no problems griding it’s mountains down to nubs they unearthed TONS of solid blocks of sandstone. Most of the older buildings have sandstone bricks/blocks and the sidewalks as well as the curbs in older neighborhoods are all sandstone. What was nice about it, is sandstone is really easy to break off in sheets and if you made them thick enough the tree roots wouldn’t break them. Saddly, they are a hazard and are slowly being replaced with concrete as they wear out. As the sidewalks age they become uneven and unusable to people who require mobility aids. Personally, I think they are an asset to the city and with a little extra work they could be re surfaced and reused. Such is life.
Denver also has an open air mall along 16th street that was designed by I. M. Pei (and others) which is composed of heavy granite tiles and suffers from all of the afore mentioned short comings. However there is a resurfacing project under way to texture the tiles . . . we’ll see how that goes
February 24th, 2010 at 2:44 pm
Great write up.
By the way there’s another reason granite should be avoided: it’s radioactive! I had a radon inspector tell me a story of taking a handful of broken quarry granite and his geiger counter went crazy. It isn’t being talked about much (yet) but at this point there’s no way I’d want granite countertops (i’d prefer quartz or recycled glass anyway) and with the costs stated above, I’m not sure I’d want to walk over miles of it either.
February 25th, 2010 at 1:04 am
Alon, the sparkly sidewalks in NYC are because the city experimented with using crushed glass in the aggregate mix for a while. They do look nice, and they are slightly more ‘grippy” on your shoes.
February 25th, 2010 at 2:20 pm
My company, the Southface Energy Institute, uses pervious concrete for our sidewalks. It is does provide great capacity for allowing storm runoff to seep through thus encouraging water to migrate back to aquifers rather than to the sewer drains, is comfortable to walk on, provides a good SRI value, and is somewhat more attractive than concrete. The porousness of the concrete allows water to seem through the surface, thus not allowing ice to collect on its surface, and also provides decent grip capacity when it rains.
However, I have found that maintenance on these surfaces is somewhat of a challenge. In the spring and fall, pollen and other tree droppings tend to get caught in the cracks of the surface, thus causing us to have to clean it with a power washer. Not necessarily the greenest solution for that matter. Also, if soil is dumped onto it, it must be cleaned somehow for the pores to remain open and for the surface to absorb water. Thus, I think it can be a great solution for some situations, but perhaps not the best material for everywhere.
February 26th, 2010 at 3:56 pm
Has anyone ever thought about replacing concrete in retail/pedistrian only areas with synthetic turf.
Advantages
- It’s asethetically pleasing to look at
- It’s low maintenance
- It’s porous so you don’t get near the run-off of concrete
- It’s made from recycled tires
- It’s has the look of natural grass without the maintenance
- B/c it’s not natural grass you won’t get grass clippings on your clothes or shoes and track it into stores
- It’s not slippery in poor weather conditions and b/c it’s fairly soft if someone were to fall it would hurt a lot less than concrete
- You can put designs on the turf just like football fields do
- You can have different colors like the blue turf at Boise State
- On hot days it’s significantly cooler than concrete
- It’s shelf life is fairly good and patch work can be done to sure up deteriorated areas
August 10th, 2010 at 10:33 pm
Pervious concrete is evolving rapidly both strength wise and production wise. I believe we will see a lot more instalations as time goes on. Perhaps exponential growth. CO2 is even being sequestered in concrete in more efficient ways that begin to offset its production. See the links below….
http://www.estesdesign.com/
http://www.stormh2o.com/january-february-2009/infiltration-clay-soils.aspx
http://www.estesdesign.com/images/FlashFlood_March2010.pdf