Switching off the engine instead of idling is one way to cut down on fuel consumption and emissions. But drivers want to stay comfortable while waiting to unload or parked for the night, and that undermines this simple strategy. If drivers can turn off the key and still stay warm in the winter and cool in the summer, idle time can be reduced by huge amounts.

Owner-operators have used auxiliary power units for a number of years to accomplish this. Of course, their decision to turn off the truck engine might have more to do with economics than environmental awareness. The same is true for fleets, which until recently have been reluctant to make that kind of investment. An APU and installation can cost from $5,000 to $10,000, and while the return on investment has shortened considerably with rising fuel prices in recent years, the costs don't pencil out for many fleets.

But some very large fleets are spec'ing APUs and touting reduced idle time and fuel consumption. Wal-Mart began equipping its private fleet with APUs about two years ago, after a settlement with the U.S. Environmental Protection Agency. The company agreed to take steps to reduce truck idling at its stores and distribution centers. According to the company's web site, the APUs saved $25.5 million a year in fuel costs at an average diesel price of $2.60 per gallon.

The company estimates cutting the engines cut CO 2 emissions by 100,000 metric tons. Wal-Mart recently announced a goal of doubling its fleet's fuel efficiency by 2015 through a number of strategies, including reducing idling, aerodynamic tractors and side skirting, wide-base tires and tag axles. Plus, the company is testing hybrid vehicles.

In June, Marten Transport of Mondovi, Wis., announced it would equip its fleet of more than 2,000 tractors with TriPac APUs from Thermo King.

According to Robert Smith, Marten's COO, the company has about 5 percent of its fleet equipped with the APUs and expects to have all the trucks ready within 18 months. Marten began testing about 18 units through a Wisconsin state program. "One of our local legislators really helped us get started with this," Smith says.

The results of the testing were startling. "We went from 40 percent idle time to as little as 2 percent idle time on those 18 trucks. At the end of the day, it was clear they could pay for themselves." Even if fuel were selling much lower than currently, Smith is convinced the units are still a good idea.

Part of the program includes training drivers on how to use the APUs. They are shown an instructional video and they sign-off when they understand how and when to use the units. "There's no point in putting them on the truck if the drivers don't know how to use them." The driver response has been very positive, Smith adds. For drivers who did not receive training, idle time fell only to about 24 percent to 28 percent. The program also includes various idle incentives and training for the office and shop.

Marten is routing about 180 to 200 trucks a month through its Mondovi headquarters for APU installation. Of its fleet of nearly 2,500 trucks, the only ones that will not get an APU are the ones slated for trade-in within the next 18 months.

Marten usually trades its trucks after four years. The company is still evaluating what to do with the APUs when they trade their newer trucks. "The APU certainly has a longer life than the truck," Smith says. "We may decide to take the APUs off the old trucks and put them on our new trucks." Or, they may find that the APUs add enough value to the trucks at trade-in that they will leave them on when they replace them.

The high price of fuel had some role in pushing the company to begin spec'ing the APUs, Smith says, adding that wasn't the prime reason the company made the decision. "Back in the early part of the discussion, fuel price was probably part of it. But if that was the only thing, we should have done this two or three years ago." Driver comfort and environmental and regulatory factors also played a role in the decision. "We've not had any issues with our non-APU trucks as far as no-idling regulations, but we can see that's probably coming down the road. We've had a couple of our larger customers express concerns, and we are certainly concerned about the regulations in states such as California."

Tom Kampf, APU product manager for Thermo King's TriPac, says fuel cost is only one of four factors leading more fleets to adopt APUs. "Probably No. 1 is driver comfort and driver retention. Fleets are also concerned about state and local regulations limiting truck idling and finally, there is a concern with a lot of fleet people about their environmental stewardship. Fuel costs are a part of it, but there's a lot more going on as well." Kampf says he has seen a surge of interest in the unit, adding "particularly over the last six months, a lot of the smaller and mid-sized fleets are starting to adopt them."

Although the U.S. Environmental Protection Agency recommends auxiliary power units as part of a plan to cut truck idling, these units may not be the ultimate answer in reducing heavy truck emissions and fuel consumption. Next year, California will require APUs be equipped with aftertreatment devices on 2007 model year or newer trucks with 2007 model year or newer engines, which will increase the costs of the units. APUs on older trucks will not be affected.

Kampf says his company will offer two options. One is a regenerative option similar to the systems used on 2007 engines. The other will be a non-regenerative solution. Other suppliers say they will have solutions available for the California regulations as well. But there are concerns in the industry that these units will cost more.

Other solutions to cut idle time include electric-powered HVAC systems, or shore power setups, that allow drivers to power HVAC and appliances from a electrical outlets at truckstops or terminals.

Whether its APUs or electric-powered units, not all will work as well for some fleets as they do for others. And while there are a number of reasons fleets may want to adopt these technologies, $3 a gallon diesel fuel probably gets the discussion started. In this sense, the high cost of fuel may be good for the environment.


The American Trucking Associations and the Canadian Trucking Alliance are urging state governments in the United States and provincial governments in Canada to revise their fuel tax systems to encourage truckers to use environmentally friendly idling reduction technology.

In a joint statement, CTA CEO David Bradley and ATA CEO and President Bill Graves asked International Fuel Tax Association Inc. member jurisdictions to stop taxing fuel used to operate idling reduction technology, mainly auxiliary power units that reduce diesel fuel consumption and greenhouse gas emissions by large truck engines. (IFTA is the organization of states and provinces through which motor carriers' fuel use tax obligations are administered uniformly throughout North America.)

The primary reason for large truck engine idling is to heat or cool the cab for long-haul drivers during periods of rest. However, several studies have clearly shown that using a heavy-duty truck engine to power the heating and cooling of a truck cab is inefficient and environmentally unsound.

"The use of idling reduction technology could reduce the fuel consumption of a long-haul tractor by some 1,900 gallons or 7,200 liters per year – which equates to an emissions reduction of greenhouse gases of some 42,000 pounds or 19 metric tons," said CTA CEO David Bradley. "The tax system has a role to play in accelerating the use of this emission-saving technology."

The cost of an APU varies with the type of device, anywhere from $6,000 to a top price of perhaps $10,000, with an average of about $7,750. Likewise, the fuel consumption of an APU will vary, but may be estimated for an over-the-road operation at 500 gallons a year. At the average state fuel tax rate of about 22 cents per gallon , an exemption would represent a tax savings of more than $100 a year in the U.S. or $280 in Canada.

"Coupled with operational savings, this is a significant incentive for installing an APU," said ATA's Graves. "Governments have a role in regulating emission reductions from the trucking community, but the public sector must also recognize its role in providing the business community with incentives to further reduce these emissions."

ATA and CTA have invited the states and provinces to meet with national staff of the trucking associations or with local associations to provide more insight into the environmental benefits associated with this proposed tax change.