Why aren't roads made out of plastic?
March 13, 2008 5:55 AM   Subscribe

Why aren't roads made out of plastic?

Just passed some road construction on my way to work, and read an article on the decaying U.S. roadways, and it got me thinking. Why hasn't there been a radical improvement in road paving materials? Why asphalt? Why not plastic? Or rubber? Or artificial turf? It seems to be materials science should have, by now, come up with something that would be freeze/thaw impervious, non-slick, and not need to be replaced every few decades. Why not a one-and-done for 200 years paving solution? Anybody know?
posted by lpsguy to Travel & Transportation (36 answers total) 4 users marked this as a favorite
 
Remember that road construction is connected to the political process. At least part of the answer is that makers of concrete and asphalt have excellent lobbyists. (Ever been to a state where the interstate is ALL concrete? That's why.)
posted by mikewas at 5:59 AM on March 13, 2008 [2 favorites]


Why not plastic? Or rubber?

UV degradation. Outside under the full sun is an uncompromising environment.
posted by OmieWise at 6:05 AM on March 13, 2008


At a newspaper I used to work for, I wrote about a company that tried to make a recycled plastic additive to asphalt, using shredded razor handles and other common trash. The heavy-handed asphalt industry pushed back, the company's founders shot themselves in the foot by complaining loudly about said industry, and the company went bankrupt soon thereafter.
posted by M.C. Lo-Carb! at 6:17 AM on March 13, 2008


Your tires are made of rubber, they need to have a substantial amount of grip. The first time it rains on a rubber or plastic highway you'd find out why they aren't built of that. I'm sure theres some sort of polymer that could be made, but it'd be far more expensive than concrete or asphalt.
posted by sanka at 6:25 AM on March 13, 2008


I read a similar article to M.C. Lo-Carb's, but about a teflon sheet that could be put down when a road was being built and the asphalt placed on top. The benefit was that it would wick away water, and could triple the lifespan of a road.

The asphalt industry hated that one too, and the technology, as far as I can tell, died.
posted by bshort at 6:26 AM on March 13, 2008


You ever drive a loaded dump truck down a rural asphalt road when it's like 98 degrees out? Notice that it leaves a wake of deformed asphalt in the path of the treads, now imagine the tires covered in melted HDPE (110-160F) that's wrapped around the axles like a taffy pulling machine. Yeah, no.
posted by prostyle at 6:34 AM on March 13, 2008 [1 favorite]


Why not a one-and-done for 200 years paving solution?

Because how we use roads is changing a lot faster than 200 years. That is, we are still using 200 year old roads (and much older), but how we use those roads is subject to quite fast change -- donkey carts to early cars to modern cars in under a century. Just to take one example, as traffic speeds increase, the need for banking and appropriately-radiused curves increases as well. Are you sure that 200 years from now we will want the same size, type, and specification of roads, going to the same places, used in the same ways? In 200 years, maybe we will all have flying cars, or we will be riding armored bicycles in a post-apocalyptic wasteland, or we will have all been eaten by giant cockroaches, I don't know.

So in some ways you could say that impermanent road surfaces are a feature, not a bug -- pavement is already an insufficiently flexible part of our infrastructure system; making it more so would not be good as we confront large-scale changes.

That is not to say that there are not improvements in road materials -- pavement that is permeable to water, or is made from recycled content, or has other attributes is constantly being developed. But it takes a long time from concept to proven product, and there is a lot of capital investment already in the machines and production capacity for currently used materials, so switching materials (say, from asphalt to plastic) would not happen overnight.
posted by Forktine at 6:35 AM on March 13, 2008 [2 favorites]


I am not a civil engineer, but some of these comments are ridiculous from any technical development perspective.

There is constant research at universities into methods of improving road life and reducing upfront cost and maintenance. I am dubious that the asphalt industry is made of Neo-Luddites shutting down every new development as it is in their interest to adapt new technology that makes it easier for them to pave roads. Additionally, government Transportation Departments are the ones who specify paving contracts; paving companies don't just get a contract to "make one (1) road". People study this subject very carefully. It's a multi-billion dollar industry filled with consultants.

There are many other factors like the cost of modifying equipment and training personnel to use a new technology, and the ability to scale experiment-sized neat ideas up to an operational system. Governments themselves often chose the method with the cheapest upfront cost instead of paving systems that have the lowest lifetime costs for budgetary reasons.

Concrete for example costs more to build but lasts longer and has lower maintenance costs--states with all-concrete interstates are making the wiser financial decision. Or are they? Concrete has different maintenance costs depending on the climate--northern states have more frost-heave and until recently concrete technology had trouble dealing with that.

As to the original question on plastics, there is some development work going on with bridges in this area, where composites like fibreglass are being used to reduce maintenance costs.
posted by cardboard at 6:56 AM on March 13, 2008 [3 favorites]


I don't have any answers, but you might want to explore the Transportation Board of the National Academies' Strategic Highway Research Program website.
posted by billtron at 7:00 AM on March 13, 2008


Interesting discussion: Why are some highways concrete and others asphalt?

Why not a one-and-done for 200 years paving solution?

Because you have to pay the bill today?
posted by smackfu at 7:01 AM on March 13, 2008


Materials like plastic and rubber are extremely expensive.

Where I live they are experimenting with Rubber Roads -- adding fragemented recycled tires to the asphalt mix.
posted by unSane at 7:09 AM on March 13, 2008


Another drawback to plastics would be cost; even if you could design a super-plastic that would meet the requirements for paving, it would not likely be cheaper than asphalt or concrete in the massive quantities needed for road building. Also, both asphalt and plastic are petroleum products, but asphalt uses components of crude oil that are not useful for much else. Finally, the aggregate in asphalt is often partly composed of wastes from other industries such as furnace slag, so it provides a way to use wastes that would otherwise have to be disposed of. (I'm starting to sound like a spokesman for the asphalt industry, but I'm not, I promise. I do have friends in the paving industry and a brother who is a civil engineer, though.)
posted by TedW at 7:13 AM on March 13, 2008


On posting I see that unsane made the same points much more succinctly.
posted by TedW at 7:14 AM on March 13, 2008


I'm not a civil engineer or anything, but plastic is rarely used for anything structural because it eventually deforms under load. It's cheap, and it's mold-able, so it's convenient for things like bottles and things that aren't load-bearing, but otherwise, you want something else.
posted by Comrade_robot at 7:19 AM on March 13, 2008


I have also heard of the teflon-beneath-asphalt story, but frankly I don't believe it. If the benefits were as great as claimed, someone would have gone for it regardless of industry opposition.

Everyone, everywhere, uses concrete or asphalt. The reason is not just industry inertia; paving is a tough nut to crack -- the combination of high abuse and low cost kills most would-be replacements.
posted by aramaic at 7:27 AM on March 13, 2008


I am a civil engineer and cardboard pretty much nailed it. The only exception being that with rising oil prices, asphalt paving can now cost about the same as concrete.
posted by Uncle Jimmy at 7:27 AM on March 13, 2008


I know that in the Netherlands they experiment with adding recycled rubber to some of their asphalt. It's apparently very good (and quiet) when it rains, but not so much when it snows. Fortunatly it doesn't snow very often in their neck of the woods.
posted by maremare at 8:02 AM on March 13, 2008


While I'm not an engineer I did work as an estimator for a concrete company in Alberta for a number of years and I agree with Uncle Jimmy's agreement with cardboard. Furthermore there are a couple of other interesting bits I can add:

Concrete in Canada tends to be rather expensive - the market is basically served by only 2 suppliers, and their wholly owned subsidiaries. Concrete paving is therefore reserved for airports, bridge decking and high use areas (like bus stops). Even in places where the weather might not favour asphalt as strongly.

Asphalt is also easy to patch and fix.

The holdback period (the warranty period, after which a holdback on the contract is paid out - usually 10%) at least in Alberta is usually 2 years for roads. The same is often _25_ for bridges. Contractors are generally required to obtain bonding for such contracts. Insurance backers and engineering purchasers are loath to trust anything too experimental. When asphalt works so well and concrete is so well understood there's very little market pressure to try anything too adventurous. For the cost, overhead, and scope involved in building a bridge there can sometimes be wiggle room to do things differently but there's still the matter of the quarter century warranty period.
posted by mce at 8:30 AM on March 13, 2008


I'm neither civil nor an engineer, but I took CE 101 and worked on a road crew paving roads for a summer - and our roads were hot tar and gravel.

I don't know why asphalt is still king, but I would imagine it is because it works well enough and because switching materials would require changing a lot of infrastructure (paving equipment) and practices (a lot of worker retraining).

See also: wood framing for houses.

Yes, paving companies do get contracts to build "One (1) road" from towns and developers.
posted by zippy at 8:43 AM on March 13, 2008


I understand that the technology is always being refined and there's an economic structure as well as well-known skills to work with current materials, but what about making changes to the cars themselves along with changes to the roads. Asphalt and concerte make a lot of sense when you have 2 ton machines riding on little strips of rubber, but are you guys honestly saying that there's no new-gen concepts for road cars? That no one has come up with a new type of wheel to run on a new type of road?

I would think that at a certain point you might just be reinventing the light rail system, but its a little surprisign to hear the consensus that concrete and asphalt with its 12-24 month lifespan and constant pot-hole filling is the best we can currently do.
posted by damn dirty ape at 9:00 AM on March 13, 2008


I'm not a civil engineer, but I am a (soon to be) librarian working at a transportation library. cardboard, Uncle Jimmy, and mce are pretty much correct from my understanding.

Reading HMAT (Hot Mix Asphalt), it's clear that there are changes in the industry being pushed by a need for longer life spans, lowering costs, and trying to be more sustainable. Many places are starting to use a combination of pavement and concrete on their road surfaces. The other hot trend is in-place recycling of the pavement, using cold or warm mixes.

Research is being done to look at how vehicles interact with the road. (I know tire-pavement noise has been a big issue.) Plastic roads sound really neat and futuristic, but also as viable as hover cars.
posted by kendrak at 9:03 AM on March 13, 2008


The biggest reason why some materials are used over others is cost. The lowest cost road is the preferred alternative by the public and politicians. Nobody cares about longevity until the road starts going to hell and then people start asking why it didn't last longer. Generally roads are designed for 20-30 year lifespans for a variety of reasons which I won't get into but which Forktine mentioned.

Material costs are obviously only one part of the equation. The actual costs of placing the material is important and is usually a bigger cost of any construction project. Brand new technologies require new equipment and techniques for efficient production. A plastic roadway would probably require an initial expenditure of millions of dollars worth of equipment and training. No contractor or public entity would take a chance on such a new technology at that huge of a cost difference. Would you as a property tax payer be willing to fork out an extra $5,000 special assessment to have a plastic road built in front of your house besides the $5k you might normally pay? Doubtful.
posted by JJ86 at 9:04 AM on March 13, 2008


I'm with cardboard, too.

I'd like to add that it's economics, primarily, which is the hidden and usually most important factor in engineering solutions.

Road design is complicated. Your average dolt driving a Colt down the highway doesn't know if he's on asphalt, glassphalt, concrete, a hybrid or what the design considerations were for the roadway. Is it a 5 year road, a 20 year road, a 50 year road? Does it take traffic from the local quarry or just car traffic? (The difference is that one overloaded truck axle is equivalent in road wear to 20,000 cars.)

It's easy to see just the surface of the road. It's nice and smooth and flat and looks like some high-tech material would be a quick and easy replacement.

What is under that surface to some degree requires engineering appreciation of issues like strength of materials, reinforcement, drainage, flexibility, thermal performance, porosity, expansion/contraction stresses, chemical resistance, coefficients of friction, ad nauseum.

If there were a clearly superior material, it would already be on the highways. There are all sorts of people working on pavement engineering nationally. UI in Urbana-Champaign has a bunch of equipment for pavement testing and evaluation (I worked on it!) and there are scores of similar places nationwide.

The amount of money needed to realize these roads we use is almost staggering. I once calculated that I would not ever earn enough money to pay for just the highway paint in the white and yellow lines on the two main interstates that run through my tiny state (Vermont)! High stress roads cost millions of dollars per mile, using dirt cheap dirt and concrete.

Look to economics for your answer. It's not some conspiratorial cabal of tar czars who call all the shots. It's the power of the purse and the miracle of optimization.
posted by FauxScot at 9:43 AM on March 13, 2008


I'm also a civil engineer and the short answer is that it's cheap, it's a proven technology and you have a large labor and business infrastructure that knows how to build roads using asphalt. Some of the newer technologies like Superpave or gap-graded aggregates are improving the quality and lifespan of roads, but the process is very similar to what we've always done. There's also a type of asphalt paving that allows water to drain freely through it, although it's not suitable for roadways and is mostly used in parking lots to mitigate stormwater runoff.

Also, note that "smooth" is not necessarily a desirable quality in a roadway. You need to be able to stop, after all.

its a little surprisign to hear the consensus that concrete and asphalt with its 12-24 month lifespan and constant pot-hole filling is the best we can currently do.

That's just incorrect. The design life for roadways is usually around 20 years, depending on the area. If your road lasts a year, then either your contractor cheated you or your inspector was asleep at the switch.

Asphalt and concerte make a lot of sense when you have 2 ton machines riding on little strips of rubber, but are you guys honestly saying that there's no new-gen concepts for road cars? That no one has come up with a new type of wheel to run on a new type of road?

I don't think you understand how the economics of things like this work. For this unspecified technology to make sense you'd have to:

1. Offer some improvement other than "Neat, plastic!"
2. Offer some economic benefit to offset the massive costs with pursuing the new technology.
posted by electroboy at 9:57 AM on March 13, 2008


There are actually roads made of some kind of mix of asphalt and rubber. They're in fairly wide use in the freeways around Phoenix. They apparently have the advantage of being longer-lasting and definitely are much quieter to drive on. link to an article about them. You can also google "rubber roads".
posted by !Jim at 10:09 AM on March 13, 2008


Offer some improvement other than "Neat, plastic!"

No need to be dismissive. My point is that there's always a next-gen concept for everything and theyre usually interesting to read. I think everyone here understands basic economies of scale, which are true, but it also true that markets and methods do get shaken up when new ideas with capital to back them enter the market. I imagine this attitude is like Henry Ford saying "The Model-T is the most amazing car ever. It does everything people need and is cheap to produce." He couldnt envision such thing like anti-lock brakes, airbags, AC, etc. Or amusing (to us) stuff like this. Everything I use today had a predecessor that was inferior, including roads (think dirt roads). The computer you are using has nothing in common to the computers in the 40's 50's and 60s. The idea that this is a solved problem and will work for thousands of years in the future is being naive.

The idea that there's no next-gen conepts for traffic is being silly. Ive already read about autonomous driving, drive by wire, and exotic materials for tires (not to mention the tweel). People already have mentioned using junk rubber as a material additive. There have to be ideas out there for roads too. I think replying with "ITS EXPENSIOVE AND DIFFERENT AND DIRT IS CHEAP ZOMG" is a valid reply of sorts but dismissing any next-gen concept as being espoused by people who think plastic is cool is being a dismmsive neo-luddite. I think he has a valid question and somewhere there are some valid answers. No need to ignore practiallity but you cannot ignore that progress happens, especially when we dont expect it.
posted by damn dirty ape at 10:13 AM on March 13, 2008


Also if you re-read his question you'll see he's asking about material advances, not "tell me why the current system is so efficient." His original question is very valid and dismissing it like so many have is really not helping in this forum.
posted by damn dirty ape at 10:18 AM on March 13, 2008


[Couple comments removed. Take it to email if you want to have a personal argument; keep the thread respectful.]
posted by cortex at 11:00 AM on March 13, 2008


All the mention of using chipped tires in roadways is kind of old. It started to become popular in the eighties and it has been found to be a poor additive for HMA roads. Even Superpave is on the old side and is starting to be nudged out. New techs currently coming of age are Green Highways and road designs based on MEPDG which is less of a mouthful to say than Mechanistic Empirical Pavement Design Guidelines. It actually takes into effect climate and neglects cars from the equation, rather focusing on the effects on truck traffic which does the most damage to roadways.
posted by JJ86 at 11:12 AM on March 13, 2008


I wouldn't say Superpave is getting nudged out. Given the glacial pace that municipalities adopt new construction methods, it's still pretty cutting edge in a lot of places. That said, a huge problem with roads is that once the specs are written, no one ensures compliance. If half of the things put in the specs were verified and tested there'd be a huge improvement in the quality of paving.
posted by electroboy at 11:33 AM on March 13, 2008


Just a little clarification on my last paragraph is that the major emphasis on current research is not on new materials but on better ways to use the existing materials. Newer mix designs and structural methods of building pavements can produce a better product than starting out with a new, untried material.

Both concrete and asphalt are excellent materials for roadways. If they are designed and built with good quality control they can last forever. Regular maintenance can extend the life and prevent potholes. Even in northern climes, if the roadway is designed and built correctly, frost heave is not an issue. cardboard folded when he said that frost heave affects concrete pavements in the north. Frost can be a problem in asphalt pavements as well as concrete. A well drained and constructed subgrade will prevent frost problems in any concrete or asphalt pavement. I have seldom seen problems with heave in most roadways.

In the future with different vehicle technology then we may need to look at different materials but until then give me concrete.
posted by JJ86 at 11:37 AM on March 13, 2008


electroboy, check out current research that the TRB is doing. This is on the verge of being adopted by many DOTs. It goes well beyond Superpave designs. I'd give Superpave another 5 years before it is history.
posted by JJ86 at 11:39 AM on March 13, 2008


I wonder if present value has anything to do with this. If you compare the cost to construct a road that will last 30 years longer vs. just building a cheaper road and saving the difference in some investments to cover building a new road in 30 years, the incremental cost to building a more durable road would have to be pretty low for a net gain.

Looking at a quick present value calculation assuming a 10% annual return, if you could build a road that would last 60 years instead of 30, it would only be worth it if that would cost less than ~6% more to build it to last an extra 30 years.

Of course this ignores upkeep which might be reduced on a more durable road, but of course, the present value of future upkeep is also pretty low.
posted by I like to eat meat at 12:42 PM on March 13, 2008


i like to eat meat, engineers always need to perform a LCCA (Life Cycle Cost Analysis) before the road is even designed to determine which is the most cost effective method of constructing the project. I use a special program to analyze the pavement design which takes into account present worth costs fifty years beyond the time of construction. It takes into account traffic projections, maintenance costs, etc. Comparisons are made between different types of pavements. It's one of the tools used to come up with the best pavement design.
posted by JJ86 at 1:01 PM on March 13, 2008


Frost can be a problem in asphalt pavements as well as concrete.

I thought the bigger issue was that snowplows take ruts out of the roadway pretty regularly, and asphalt is a lot easier to repair.
posted by smackfu at 1:01 PM on March 13, 2008


smackfu said: I thought the bigger issue was that snowplows take ruts out of the roadway pretty regularly, and asphalt is a lot easier to repair.

Not really on both counts. Ruts aren't too big of an issue in the north unless the asphalt is really crappy. The only time I see them is where there are bus stops and new stops are typically put in with concrete for the last ten years or so. Where there are ruts I've never seen a plow take them out. Asphalt can be cold patched as easily as concrete when you have potholes. A newer method used on potholes is a quick-set, smaller aggregate slurry which is really nice. It's used on concrete or asphalt pavements.
posted by JJ86 at 1:30 PM on March 13, 2008


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