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How stiffer pavement could save millions of barrels of oil

By | May 24, 2012, 3:02 AM PDT

A recent study conducted by civil engineers at MIT found that using stiffer pavements on U.S. roads could cut vehicle fuel consumption by as much as three percent. That savings could add up to 273 million barrels of crude a year.

Stiffer roads also would reduce annual carbon dioxide emissions by 46.5 million metric tons, according to the study released in a recent peer-reviewed report. There’s no shortage of road studies. This is the first to use mathematical modeling rather than roadway experiments to evaluate the effect pavement deflection has on fuel consumption across the entire U.S. road network, MIT said in a release.

The study’s authors, Professor Franz-Josef Ulm and student Mehdi Akbarian, modeled the physical forces that occur when a rubber tire rolls over pavement. They contend that the energy is dispersed so that the maximum deflection of the load is behind the path of travel. This makes the tires on the vehicle drive continuously up a slight slope — and in turn, increases fuel use. Just like it takes more energy to walk in sand than on a hard surface, cars use more fuel when there’s constant upward slope to deal with.

Road roughness and deflection are responsible for an annual average extra fuel consumption of 7,000 to 9,000 gallons per lane-mile on high-volume roads in the 8.5 million lane-miles that make up the U.S. network. The authors says up to 80 percent of that extra fuel consumption could be reduced through improvements in the basic properties of asphalt, concrete and other materials used to build roads.

The research was conducted as part of the Concrete Sustainbility Hub at MIT, which is sponsored by the Portland Cement Association and the Ready Mixed Concrete Research & Education Foundation and has a goal of improving the environmental footprint of that industry, MIT said.

The authors say the study isn’t meant to pit asphalt against concrete. However, they also say stiffer pavements can be achieved by improving the material properties, increasing the thickness of the asphalt layers, switching to a concrete layer or asphalt-concrete composite structure, or changing the composition of the sublayers of the road. Concrete has its own problems. Its massive use contributes about 5 percent of global carbon dioxide production.

Photo: Stock.xchng user jovas167

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Kirsten Korosec

About Kirsten Korosec

Kirsten Korosec is a contributing editor for SmartPlanet.

Kirsten Korosec

Kirsten Korosec

Contributing Editor

Kirsten Korosec has written for Technology Review, Marketing News, The Hill, BNET and Bloomberg News. She holds a degree from Northwestern University's Medill School of Journalism. She is based in Tucson, Arizona.

Follow her on Twitter.

Kirsten Korosec

Kirsten Korosec

Kirsten does not have financial holdings that would influence how or what she covers.

She writes for SmartPlanet and is not an employee of CBS.

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0 Votes
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Interesting, but it will never happen.
So if we get rid of the scam that is asphalt roads repaved every 5 years and go back to concrete roads that last for decades we will get better gas mileage. Sounds good here.

Oh wait. That will never happen.

To keep the numbers simple, why should the taxpayers pay a government contractor $100 every 20 years when politicians can spend $60 of our tax money every 5 years to do the same thing.

How stupid of me to think about a government controlled scam in a logical manner.

I am sorry for my momentary lapse in real world logic when I actually thought this idea stood a snowballs chance in hell of happening.
Posted by Hates Idiots
24th May
+2 Votes
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I'm not quite that cynical about it.
From what I've read in the past regarding my area, a given depth of asphalt lasts about as long as the same depth of concrete, but it could depend upon local conditions. We don't have a freeze-thaw cycle here, so maybe it doesn't matter. The concrete highways need a lot more patches than I would expect. However, you're right in that they might very well be penny-wise and pound-foolish, especially in a down economy when they figure they'll be able to spend the money to do it right later, and just need to get it done now.

For awhile they were using recycled tires in the asphalt mix, and it seems to have held up in the stretch where I've traveled on it, but I haven't seen it anywhere else, so maybe it isn't working out. It makes a very quiet highway!
Posted by AlanLaRue
24th May
+2 Votes
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Consider the reduced control aspec
Making asphalt roads harder may reduce the friction factor, which will result in an increase in the number of rear end collisions and cars sliding out of control. I think we are all aware of the increased risk of slipping on concrete versus asphalt, especially when it is wet. I hope the asphalt formulation will take that into account.
Posted by bob@...
24th May
0 Votes
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I've seen this in action
I normally drive with my average mpg displayed on the driver information center rather than the odometer, just so I'll be aware of how efficiently I'm driving. The displayed value isn't really accurate, but it's a good guideline.

There's one highway I drive on occasionally, Texas State Highway 73 between Winnie and Port Arthur, Texas, where the displayed average always goes down. I can slow down to 60 mph there and not get the same mileage as I got on I-10 at 70 mph.
Posted by AlanLaRue
24th May
+5 Votes
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Things are not that simple
I'm a transportation scientist working in the area of pavements.

Roads are designed to give a certain lifetime under a predicted cumulative loading. So, if a roadway is expected to accumulate heavy truck traffic vs mostly passenger vehicles, it's likely to be made thicker and likely to be made of concrete vs asphalt. There are many other considerations, of course, such as climate, use of salt, local materials, etc. But the main idea is there is a life cycle cost analysis done that compares designs of different thicknesses and material types vs expected traffic, cost and frequency of repair, etc.

In the end, politics decides what's done. A list of priorities is prepared, with options such as "do this right for more money now" vs "let's do this cheap and maybe in five years when we have to fix it we'll have more money budgeted to DOT."

There's also an important difference between structural integrity and ride. No overlay (which will restore ride quality) will last long if the structure below has failed. Drivers notice the ride quality, engineers concern themselve with structural integrity as well, since the riding surface will have to be repaired much more often at greater expense.

In nearly all cases Portland Cement concrete (the white stuff) gives a better lifetime cost than asphalt (the black stuff, which is also concrete, btw). That's why you see it used in urban areas where there's lots of traffic and heavy trucks.

On the matter of stiff vs flexible riding surface: asphalt stiffness decreases with heat and increases in cold weather. So the asphalt designer must design the mix to not be too soft in hot weather (rutting and flushing will occur) and not too stiff in cold weather (cracking will occur). It's a difficult balance in some areas.

Finally, softer asphalt gives a softer, quieter ride (especially the new PFC or open graded asphalts, which are 20% air) and a safer ride, both in terms of friction and wet weather (for PFC) where hydroplaning and blinding splash and spray are eliminated. User costs, including loss of lives, property damage, tires, pollution, etc. are always considered.

Professional courtesy keeps me from commenting too much on the statement that MIT is the only agency to create a mechanistic model for fuel consumption vs pavement stiffness. Hopefully, the writer misunderstood or simplified that comment. If not, I'll be glad to give the MIT researchers a lengthy list of publications on the subject they should already have fromt their literature seach.
Posted by MrKnobs@...
24th May
0 Votes
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Mix?
Hmmm.. sound like some sort of mix, say, Portland (or one of the new 'super' varieties), plus tire rubber, plus glass (what Iran, of all places, has been working on, I believe) could give 'stiffness,' plus traction, wear resistance, and recycle utilization.. but that's a hip shot, of course...
Posted by friedsonjm@...
31st May
+1 Vote
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Hard and shiny
Hard and shiny, with hard and shiny tires would give great mileage. The big problem is that it does not lend itself to traction, which is friction. No friction, no stopping power. You want hard and shiny? That is what railways use.
Posted by 16Tons
25th May
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