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New aerodynamic fairings could decrease Class 8 truck fuel consumption by 7-12%

Components of the UnderTray system. (A) Front Tray Fairing; (B) Axle Fairing; (C) Rear Diffuser; (D) Aerodynamic Rain Gutter; (E) Side Fairings. Nose Fairing not shown. Click to enlarge.

BMI Corporation, in partnership with the Department of Energy’s Oak Ridge National Laboratory (ORNL), has designed a SmartTruck UnderTray System, a set of integrated aerodynamic fairings that improve the aerodynamics of 18-wheeler (Class 8) long-haul trucks and reduce their fuel consumption.

With installation of BMI’s SmartTruck UnderTray System to improve the aerodynamics of Class 8 long-haul trucks, the typical big rig could achieve fuel savings of between 7 and 12 percent, easily meeting the new California Air Resources Board mandate that calls for a minimum mileage improvement of 5 percent, the company says.

If all 1.3 million Class 8 trucks in the US were configured with these components, companies could achieve annual savings of 1.5 billion gallons of diesel fuel—approximately equal to $5 billion in costs—and reductions of CO2 by 16.4 million tons.

The UnderTray components that are part of BMI’s initial SmartTruck Phase I products are available with new equipment or as a retrofit.

Current tractor trailers have a vehicle drag coefficient of between 0.58- 0.62. By contrast, a typical car has a coefficient of about 0.3-0.35, with low drag cars coming in around 0.26. BMI’s Phase I drag coefficient target is 0.45; Phase II target is 0.35; and Phase III target is 0.25.

Using ORNL’s Cray XT-5 “Jaguar” supercomputer shortened the computing turnaround time for BMI’s complex models from days to a few hours and eliminated the need for costly and time-consuming physical prototypes. In all, running simulations on Jaguar allowed BMI to go from concept to a design that could be turned over to a manufacturer in 18 months instead of the 3½ years they had anticipated.

BMI’s work with the Department was made possible through ORNL’s Industrial High-Performance Computing Partnerships Program, supported by the Department’s Office of Science. Through this effort, BMI was able to access Jaguar, which has a theoretical peak computational capability of 2.3 petaflops (2.3 quadrillion mathematical operations per second) making it more than 100,000 times more powerful than a typical home laptop.



Since long haul large tractor trucks and trailers do most of their traveling at high speed (70 mph), improved aerodynamics is important to reduce fuel consumption. However, it will not be done unless operators are convinced that they can save $$$ doing it. Nothing else really matters to them.

Making more aerodynamic cars, small trucks, buses, tractor trucks and trailers should not cost that much more, if any at all.

Higher fuel cost (taxes) could be one of the best way to convince every body to adapt.


10-12% fuel economy improvement seems pretty realistic. I'm guessing that, in bulk, all the components would cost ~$3000/truck to produce. You're looking at $3.9billion to retrofit our entire fleet. That's easily recouped inside 18 months. The DOE should provide low cost financing and loan guarantees on the order of billions for something like this.


Is this technology new? How many years have semis been on the road --- and no one has come up with aerodynamic container attachments before? Please. Shipping costs, which include fuel costs for the shippers, are ultimately passed on to consumers so the market pressures on shippers are different than retailers. I doubt shipping companies will instantly adopt this technology...if an enterprising shipping company adopts the technology and begins charging less for shipping & becomes more competitive - it might become adopted on a larger scale. Otherwise, government mandates would be required - and who wants the government doing more and regulating more at this point given the failures of the Obama administration and the democrats?


So what you saying ejj, is that if individuals arn't willing to change behavior on their own accord, we shouldn’t bother with it?

I agree, Government is nothing but a thorn in my side. I want oil companies to profit and not be accountable for environmental destruction. God forbid if policy is enacted to help mitigate the environmental externalities that are simply to diffuse for any individual to value and internalize..


Other people have looked at adding fairings at the back for the trucks with boat tails etc.
This work would compliment it.
I suppose the trick is to make aerodynamic improvements that still allow operators to open the doors and remove the containers etc. easily.
Another thing would be to make the trucks platoon or drive automatically, so they wouldn't have to go so fast (really!).
If a human is driving, he will want to do 70+.
If a machine is driving, it will be happy to do 60 all day.


Aerodynamics on commercial trucks have to be serviceable as much as they need to be effective. These seem to fit both those requirements.


Good points ejj. Since the trucking industries can so easily pass fuel cost to customers (us), they have no real incentives to reduce fuel consumptions. Banks had a similar issue with rising house prices. The higher the better for them.

This may be a case where government intervention is required. CAFE was introduced to reduce fuel consumption (and GHG) from cars and light trucks. A similar progressive approach may be required for buses and large trucks. Fuel per tonne/miles for large trucks and fuel per passenger seat/miles for buses could be used as base factors.


I was only thinking of the possible incentives for getting shippers to adopt the technology. I'm skeptical that normal market forces would apply because shipping is simply passed on to consumers in retail prices. If the price of diesel was relatively stable, then this aerodynamic tech would be more attractive from a competitive standpoint --- but the never ending fluctuating cost of diesel would probably de-incentivize investments in the technology. So that leaves government....which has been a complete disaster around the world recently.

Dave R

You guys are forgetting about competition.

FedEx has a huge incentive to reduce operating costs because they compete with UPS.

If FedEx can reduce fuel consumption from 10 mpg to 11 mpg at a cost less than the cost of fuel - that's a huge benefit.

Just look at how the shipping companies optimize routes - for example, they typically plan routes to avoid left turns - because routes with right turns tend to get you there quicker while burning less fuel.


This is a good idea but the best way to improve the efficiency of a truck is to ship by train instead ;)


Re: diesel fuel prices and incentives

The government could provide low cost loans/loan guarantees to Class 8 truck operators. The government could also provide fund matching for a company like BMI, up to a certain amount, for investment in a domestic manufacturing facility to produce the components. Then, to incentivize the switch, the government could raise the tax levied on diesel fuel which would recover any outlays made by the government.

The net result would be lower fuel consumption domestically which would mean fewer dollars flowing out of the country to buy oil. The consumer would end up having more buying power as fuel would be less expensive/more available on the world market which would lower the cost of certain imports.

Alternately, the government could use the fuel tax revenues to add to the Strategic Petroleum Reserve. This would keep prices high while assuring that fuel consumption is lower (no "leakages" where the fuel is used in other economies) and it would give us an additional cushion in the event of war or a market that has gone haywire.

With all of that said, I'm largely opposed to government intervention (seriously, I am). The government created the housing mess with Fannie and Freddie by keeping interest rates artificially low. Tons of externalities have resulted from this including a less mobile (and therefore more easily exploited) workforce. I would much prefer a company like Exxon or Chevron to use their piles of cash and political clout to move forward simple energy conserving devices such as fairings on Class 8 trucks.

Exxon/Chevron could retrofit the entire U.S. class 8 truck fleet without breaking a sweat. How do they make money? Rent the fairings out or offer a fuel discount for trucks that use the fairings. Companies like Exxon/Chevron need to stop being oil and gas companies and start being energy companies (Chevron is on to this already to a small degree).


GP. Do you seriously believe that Exxon/Chevron and friends would do anything to lower diesel consumption? The reverse may be more likely. I doubt that they would shot themselves in their feet.


If you've been on the roads much lately, you've probably noticed that lots of semi-trailers are sporting aerodynamic skirts down the sides. The system of front tray, axle and diffuser fairings would appear to be an incompatible scheme. The full side fairings have the virtue of keeping the slipstream from striking the trailer wheels directly, so I would not be surprised if they are more efficient.

The gutter and side fairings work with either. What might help is a truncated inflatable boat tail mounted to the trailer doors, perhaps with active control of the airflow around the transition to achieve minimum base drag.

Coke Machine

These should stand on their own merit. If they work, the truck/fleet operator will buy them. If they don't work, they won't. Taxes should be left completely out of this equation.

fred schumacher

This technology shows just how critical the airflow under a vehicle is to its coefficient of drag. It's a good start.

In the long term, what's needed is a complete rethink of the semi-tractor trailer.

Except for bulk cargo, the shipping container has come to dominate long distance transport. A shipping container is a structural beam made to carry its own load. It does not require a trailer.

If a semi tractor were to grapple on to the front of the container, with a trailing axle behind the container, the whole unit could be dropped by three feet, reducing frontal area by 25 square feet and also reducing the quantity of air flowing under the rig. Hydraulics could be used to raise the trailer to dock height.

This would also reduce the number of moving parts requiring maintenance. The container would be left bare with its axles and wheels being "borrowed" from the tractor.

In the next step, tractor locomotion could be shifted to a battery-buffered concept utilizing super-efficient, slow-turning, long stroke marine style diesels. Short-term high power demand would be handled by battery storage, with the diesel running continuously over a narrow power band. Drive would be by hub motors on all axles. Since the trailer's axles are provided by the tractor, this system would be workable without excessive increase in cost.


Fred, you're right that a shipping container is a structural beam made to carry its own load but the reason this does not happen is the flat-bed trucks that now carry shipping containers have the ability to carry other loads so they are more flexible in service.

Also, a shipping terminal is a very busy place and there's little time to spare for unloading the rear wheels from the back of the tractor unit, rolling them around to the back of a shipping container, attaching both while they are held at the right height, and then doing the whole thing in reverse to drop another shipping container off.

With a flat-bed all a truck driver has to do is drive under a crane and stop for a minute while the shipping container is lowered and the lock-downs are secured.

fred schumacher

Re: "a shipping terminal is a very busy place and there's little time to spare for unloading the rear wheels from the back of the tractor unit"

That's true. However, the whole process could be automated with hydraulics.

Some years ago I rode on a logging truck hauling tree-length pulp wood. The "trailer," consisting of a long tube with the back axles attached, collapsed and folded up, the entire assembly resting on top of the fifth wheel when in transport position. The whole thing was handled with hydraulics. The driver did not have to get out of the cab.

Something similar could be designed, automating the hook up process. Another advantage of such a system is the lower center of gravity. I once rolled a fully loaded grain truck when I backed one side into a big pot hole I couldn't see. It's no fun.


I was going to say much of what Fred said, but there are a couple of details.

  1. The length limit of OTR trucks in most states is 65 feet. If you put the tractor's wheels ahead of the container and the rear wheels behind, a 40-foot container doesn't leave much room for the tractor.
  2. The weight limit of the standard 40-foot container is greater than most state truck limits, so they'd have to be under-loaded.
Other than that, it's a great idea. Maybe you could finesse the length issue with a tractor designed to carry the container as a unitary truck (not semi-trailer) using all-driven wheels up front.

Tony Chesser


Truckers are paid by the mile. More miles/hour = more $/mile. So, naturally, they want to go as fast as possible.

Also, count in the fact that they're only allowed to be "on duty" for a certain number of hours within a week, within 24 hours, etc. For more specific information, see:

Consequently, if they're doing 60 instead of 70, that limits how far they can go before they have to pull over and rest.

For many routes, that's the difference between delivering in 14 hours and delivering in 24+ hours (with a mandatory break along the way) or delivering in 38 hours vs 48+ hours (60 mph * 14 hours = 840 miles; 70 mph * 14 hours = 980; rules require <= 14 hours on + >= 10 hours off in any 24 hour period). Consequently, reducing speed results in shipments taking significantly longer to arrive (not in the shipper's best interest) or drivers bending the rules and getting "creative" in their log books (not in the best interest of others who are sharing the road with that truck).

Shipment companies are hesitant about imposing corporate speed limits, but some of them do. SWIFT trucking routinely puts governors on their rigs. That's why many drivers refer to them as Slow Wagons In Fast Traffic or Sure Wish I had a Faster Truck.

No, I'm not an OTR driver. My dad was. His company toyed with putting governors on their trucks. Lower speed = higher fuel mileage, after all. Once dad explained that the proposed governor setting would result in this trip taking 25 hours vs 14 (because the lower speed would result in a mandatory rest period between pickup and delivery + another hour of travel time) and other variations on the theme, they backed off.


Tony, that's why we need something like the combination of Blade Runner dual-mode trucks (on electrified rail) and Google's automated driving system (which only needs cruise control for trucks on rail). A driver going 70 MPH can cover 980 miles a day on road, but a truck on rail able to roll even with the driver asleep could cover 1680 miles a day. Even if you pull the rail back to 60 MPH it still goes 1440 miles a day, 460 more than the faster truck on pavement.

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