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Study: Improvements in Large Truck Aerodynamics Could Save US Nearly One Billion Gallons of Fuel Annually

The widespread application of new aerodynamic technologies on tractor-trailer trucks could cut US fuel consumption by nearly one billion gallons per year, according to the results of a two-year collaborative study conducted by members of the Truck Manufacturers Association (TMA) and the US Department of Energy (DOE).

Four TMA members—International Truck and Engine Corporation, Freightliner LLC, Mack Trucks, Inc. and Volvo Trucks North America—representing 75% of the US market for Class 8 trucks teamed with the DOE to study a variety of design improvements that would reduce aerodynamic drag and significantly improve fuel efficiency.

Technologies that improve truck aerodynamics in several key areas include:

  • Gap Enclosure: reduces aerodynamic drag in the gap between the tractor and trailer.
  • Side Skirts: improves aerodynamics and reduces airflow under the trailer in crosswinds.
  • Boat Tails: tapers back of trailer to minimalize wake airflow.
  • Side Mirror Design: reconfigures shape and support systems to reduce aerodynamic drag.

The combined effect of all aerodynamic improvements on one vehicle could result in as great as 23% reduction in aerodynamic drag. For every 2% reduction in aerodynamic drag, there is a 1% improvement in fuel efficiency.

To put this in perspective, if every tractor/van semi-trailer combination truck in operation in the US adopted these technologies and improved fuel efficiency by 10%, it would translate into nearly one billion gallons per year of fuel savings. These small improvements collectively could make a huge difference in reducing fuel use.

—Robert Clarke, president of the Truck Manufacturers Association

The calculation of one billion gallons is based on the Census Bureau’s 2002 Vehicle Inventory and Use Survey (VIUS). It assumes 750,000 tractor/van semi-trailer combination-unit trucks in operation traveling a total of 60,101 million miles. A 10% improvement in average fuel economy from 5.5 mpg to 6.05 mpg results in saving approximately 993.4 million gallons of fuel per year.

The two-year study was funded by the US Department of Energy FreedomCAR and Vehicle Technologies Office through the National Energy Technology Laboratory. The Truck Manufacturers Association is a not-for-profit technical trade association headquartered in Washington, DC. Members are corporations with principal headquarters located in North America who engage in the design, development, manufacturing, marketing and sale of Class 6, 7, and 8 medium and heavy-duty trucks.



Cool. Isn't this the kind of stuff Amory Lovins and RMI are doing with Wal-Mart? And wouldn't rail freight be even better?

Harvey D.

TGV train in Europe is already very aerodynamic. Of course, it cruises at 350 Km/hr. No more R & D is required. These trains have been rolling for almost 15 years.

Its amazing that we now realize what we have known for decades.

Lou Grinzo

The key here is that we needed a sufficiently large incentive to overcome inertia. It costs at least a little to make such changes, and businesses tend to be extremely reluctant to make any change unless they're convinced it will have a favorable payback. With current fuel prices and numerous predictions that they're headed higher for years to come, the businesses are getting the hint that it's time to take at least minimal action.

Like everyone else here, I wish companies were more aggressive in adopting such obvious techniques to increase energy efficiency.


The key here is that we needed a sufficiently large incentive to overcome inertia.

Here's some. Choose the ones you like:
* higher fuel taxes
* increased "CAFE" standards on the cabs
* increased DOT regulations on skirts (they're also much safer when a car hits the side of a jack-knifed trailer)
* subsidies to help make the fixed cost transition for cabs or trailers built in tUSA


How about taking a cue from Chrysler's Bionic car inspired by the boxfish? Seams like they got a minivan to be aerodynamic.


Or when a drunk driver weaves into a semi. For these purposes, the side skirts should be built:
a) strong enough to keep cars from getting under the trailer.
b) be weak enough not to crush a car against a concrete divider, or crush the roof in on the side of the smaller, shorter vehicle when the side skirts pivot/crumple upwards.

James Mahon

a: This is great stuff.
It is practical in that most truckers could do this right away - they do not have to buy new rigs.

b: Do we have a breakdown for each enhancement ?
Cost as well as drag gains.

c: What if they just slowed down 5 mph ?

d: following the jn2 comment - has anyone done this study for goods trains ?

Fat Knowledge

At 60.1 billion miles and 5.5 mpg that works out to 10.9 billion gallons of fuel a year. With 300 million Americans that comes to 36 gallons of fuel per person. This savings would bring that down to 32 per person.

As large as 1 billion gallons sounds, keep in mind that the US uses around 150 billion gallons of gasoline a year, so this would be less than a 1% savings. But, save a billion gallons here, a billion gallons there, and all of a sudden you are talking real savings. :)

Robert Schwartz

Get rid of rear view mirrors, replace them with tv cameras.


I thought aero was a relatively small contributor to drag in heavy goods vehicles compared to cars. Attention to rolling resistance is also required (eg low CR tyre research).


Robert Schwartz,
Keep the mirrors for redundancy, but have them:
a) folded into an aerodynamic form
b) have them tucked way/stored, ready to deploy on the fly
If you travel 20,000-50,000 miles a year at 50-70 mph, it adds up.

Eric Purinton

I think we should pass a new traffic law in the United States, I know they have a similar law in Germany. A law that would outlaw any semi-truck, dump-truck or any vehicle towing anything from using the far left lane on interstates and highways. If theres two lanes going in one direction, those vehicles must stay in the right hand lane. If theres 3 lanes going in one direction, those vehicles must stay in the middle and right hand lane (and out of the far left passing lane).

On the Autobahn it's crucial for the flow of traffic not to have a semi-truck traveling at 90kmph being passed by another semi-truck traveling 95kmph.

That would slow down some of the largest and most fuel inefficent vehicles on the road, decreasing their gas consumption. It would also decrease (albeit a small degree) the fuel consumption of regular cars on the road who constantly have to slow down and then speed back up when these semi-truck drivers think their big rig has a big #8 on the side (nascar reference) and that I-435 is the Talladega Superspeedway when they're going 3 wide (3 semis side by side by side blocking all the other vehicles behind them).



Traffic laws are dictated by the states. Some states do restrict these vehicles to the right most lanes.

These vehicles have a very large frontal surface area and high Coefficient of Drag. Even though the weight is a primary loss of efficiency the aerodynamic drag is much more substantial than any passenger vehicles.


I got an idea. Lets get NASCAR to sponsor Class-8 truck racing ;-)


it's funny how studies like this get published on the GCC every few months. isn't it about time someone actually implemented the suggestions these studies recommend?


Paccar is instituting some changes (APUs):

P Schager

Video cameras are so cheap now that you might as well put several in, for enough redundancy that the pop-out backup mirrors are almost mere security blankets. Use two or more displays in the cab (glass cockpit) and suitable redundant electronics design. This would be better than mirrors, because of all the vantage points you can cover. Cameras could be steerable, maybe automatically to follow the lanes. Software could help with the image analysis, alerting the driver when new vehicles have moved in around him, indicating their relative speeds and so on.

The aerodynamic tweek forms could largely be done with inflatable structures, for light weight, easy design, and adaptability. Easily collapsed for dead-heading, for instance.

All this should have been done years ago. Nobody's in charge who cares.


hi my names blake im doing a science project and i choose aerodynamics and i need some info and diagrams and i was wondering if you could help me i am especialy like the studies on trucks you made from blake.


hi my names blake im doing a science project and i choose aerodynamics and i need some info and diagrams and i was wondering if you could help me i am especialy like the studies on trucks you made from blake.

marshall franzman

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Chuck Kottke

I was thinking about this the other day as well - all the trucks on the road, and Diesel is expensive - it would make the operators happy as well!! I think a hybrid concept is long overdue with semi tractors - looking at all the emission problems when trying to squeeze that much instantaneous power out of an engine, and then energy costs - it would make sense to have a bank of carbon nanotube supercapacitors, lithium ion batteries, and an electric motor to give the boost required. Smoothing the undercarriage as well would help, I wonder if this was considered in the analysis?? And rolling friction (tire resistance) must by very significant with semis as well - if the trucks were made lighter with aluminum-steel composite construction, and given a variable spoiler to increase traction on-demand (under high-wind conditions), this could help reduce the energy consumption as well. Just ideas! Plaster the trailers with solar cells, and pump the juice into the hybrid system!! It might not be all that much energy, but probably worth it in the long run - every drop adds up to a gallon in the end.

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