Article - Stiffer roadways could improve truck fuel efficiency

[Ecky]

I had read that concrete roads delivered higher fuel economy, but I had never stopped to consider why.

https://techxplore-com.cdn.ampprojec...fficiency.html

Every time you hear a deep rumble and feel your house shake when a big truck roars by, that's partly because the weight of heavy vehicles causes a slight deflection in the road surface under them. It's enough of a dip to make a difference to the trucks' overall fuel efficiency.


Now, a theoretical study by MIT researchers suggests that small changes in roadway paving practices could reduce that efficiency loss, potentially eliminating a half-percent of the total greenhouse gas emissions from the transportation sector, at little to no cost.

The findings are detailed in a paper in the journal Transportation Research Record, by MIT postdoc Hessam Azarijafari, research scientist Jeremy Gregory, and principal research scientist in the Materials Research Laboratory Randolph Kirchain. The study examined state-by-state data on climate conditions, road lengths, materials properties, and road usage, and modeled different scenarios for pavement resurfacing practices.

They found that that one key to improving mileage efficiency is to make pavements that are stiffer, Kirchain explains. That reduces the amount of deflection, which reduces wear on the road but also reduces the slightly uphill motion the vehicle constantly has to make to rise out of its own depression in the road.

"When we as individuals walk on pavements, they seem like perfectly rigid things. They're not responding to us," he says. "But for trucks, that is not the case. There is enough of a deflection in that surface that some amount of energy is expended to overcome the little divot that you create as you drive along." He likens it to the difference between walking on a hard surface versus walking on sand, which takes more effort because you sink in with each step.

Looking to the future, Kirchain says that while projections show a slight decline in passenger car travel over coming decades, they show an increase in truck travel for freight delivery—the kind where pavement deflection could be a factor in overall efficiency.

There are several ways to make roadways stiffer, the researchers say. One way is to add a very small amount of synthetic fibers or carbon nanotubes to the mix when laying asphalt. Just a tenth of a percent of the inexpensive material could dramatically improve its stiffness, they say. Another way of increasing rigidity is simply to adjust the grading of the different sizes of aggregate used in the mix, to allow for a denser overall mix with more rock and less binder.


"If there are high quality local materials available" to use in the asphalt or concrete mix, "we can use them to improve the stiffness, or we can just adjust the grading of the aggregates that we are using for these pavements," says Azarijafari. And adding different fibers is "very inexpensive compared to the total cost of the mixture, but it can change the stiffness properties of the mixture significantly."

Yet another way is to switch from asphalt pavement surfaces to concrete, which has a higher initial cost but is more durable, leading to equal or lower total lifecycle costs. Many road surfaces in northern U.S. states already use concrete, but asphalt is more prevalent in the south. There, it makes even more of a difference, because asphalt is especially subject to deflection in hot weather, whereas concrete surfaces are relatively unaffected by heat. Just upgrading the road surfaces in Texas alone, the study showed, could make a significant impact because of the state's large network of asphalt roads and its high temperatures.

Kirchain, who is co-director of MIT's Concrete Sustainability Hub, says that in carrying out this study, the team is "trying to understand what are some of the systemic environmental and economic impacts that are associated with a change to the use of concrete in particular in the pavement system."

Even though the effects of pavement deflection may seem tiny, he says, "when you take into account the fact that the pavement is going to be there, with thousands of cars driving over it every day, for dozens of years, so a small effect on each one of those vehicles adds up to a significant amount of emissions over the years." For purposes of this study, they looked at total emissions over the next 50 years and considered the reductions that would be achieved by improving anywhere from 2 percent of road surfaces to 10 percent each year.

With a 10 percent improvement rate, they calculated, a total of 440 megatons of carbon dioxide-equivalent emissions would be avoided over the 50 years, which is about 0.5 percent of total transportation-related emissions for this period.

The proposal may face some challenges, because changing the mix of materials in asphalt might affect its workability in the field, perhaps requiring adjustments to the equipment used. "That change in the field processing would have some cost to it as well," Kirchain says.

But overall, implementing such changes could in many cases be as simple as changing the specifications required by state or local highway authorities. "These kinds of effects could be considered as part of the performance that's trying to be managed," Kirchain says. "It largely would be a choice from the state's perspective, that either fuel use or climate impact would be something that would be included in the management, as opposed to just the surface performance of the system."

[rmay635703]

Rough roads deliver lower fuel economy

Most concrete roads around here feel like riding a horse.

Gotta wonder when the two metrics overlap

[redneck]

.

Concrete is king.

Asphalt is considered to be a flexible water barrier. Nothing more.
The underlying compaction material in addition to the soil and or rock beneath is what supports it.

Usually poorly...





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[redpoint5]

I've heard concrete makes the most sense. Then I've been on LA freeways with poor suspension and wondered why they don't maintain their roads.

What about concrete strips where the tires mostly travel, and asphalt everywhere else?

[MeteorGray]

I hate concrete roads when the slabs begin to sink at different rates and it feels like the car is jumping curbs. That's got to take a bit more energy to roll over, and in any case it surely increases the wear and tear on the vehicle.

[rmay635703]

Originally Posted by MeteorGray

I hate concrete roads when the slabs begin to sink at different rates and it feels like the car is jumping curbs. That's got to take a bit more energy to roll over, and in any case it surely increases the wear and tear on the vehicle.

Any place there is snow that is the expected driving experience after a year or two

[oil pan 4]

If the concrete road dips every car length or 2 it was usually made by incompetent and/or union labor.

[GreenTDI]

Originally Posted by oil pan 4

If the concrete road dips every car length or 2 it was usually made by incompetent and/or union labor.

Or it's a very old road that was never maintained. There is actually a 14 mile stretch of road that called 'highway to hell' here in Belgium. The N67 from Eupen to Monschau is a concrete road from 1936. Sustainability takes on a new meaning with this one. It's a real hell to ride (especially with 40+ psi in the tires) but it has become an attraction.

https://www.youtube.com/watch?v=rhl_6q8-mDg

[MeteorGray]

Those roller coaster roads are bad on cars, but try driving on one in an articulating vehicle like my F250 truck hauling an RV trailer. They can get into an asynchronous cycle that is outright funny if it weren't so dangerous.

I believe the worse was when I was driving on I-40 through Oklahoma City a few years ago. I hit a particularly bad stretch of uneven concrete slabs while hauling a 27-foot RV trailer, and the combination of truck-and-trailer was bucking so badly I literally was banging my head on the roof of the truck. Coffee everywhere. Noise and motion coming from myriad flying objects in the cabin. I would have lost control if I wasn't being held down by seatbelts.

Crazy.

[Ecky]

Originally Posted by GreenTDI

Or it's a very old road that was never maintained. There is actually a 14 mile stretch of road that called 'highway to hell' here in Belgium. The N67 from Eupen to Monschau is a concrete road from 1936. Sustainability takes on a new meaning with this one. It's a real hell to ride (especially with 40+ psi in the tires) but it has become an attraction.

You must have really good roads in Belgium!

Last time I was in Michigan, your "Highway to hell" would have been one of the better maintained roadways in that state.