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Fuel EfficiencyFuel Efficiency

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On August 9, 2011, the first set of fuel efficiency standards for heavy duty vehicles was announced by EPA. On August 16, 2016, EPA and NHTSA jointly announced phase 2 of the program, covering the 2018-2027 model years. This page contains a summary of those regulations, plus additional information on factors affecting fuel efficiency for road transportation.

Who is covered by the regulations?

The standards apply directly to engine, vehicle, and equipment manufacturers. Although the standards do not explicitly cover owners and operators of vehicles, they will affect them indirectly, since equipment purchased now will be in service during years when fuel costs and environmental regulations are likely to change significantly.

What is the purpose of the regulations?

Transportation consumes about 2/3 of the oil used in the U.S. every year, much of which is imported. In addition to saving money, improvements in fuel efficiency help reduce this dependence.

In addition to regulatory programs, EPA provides voluntary programs, such as SmartWay, to help industry make the most effective use of available technology and financing to improve fuel efficiency and reduce fuel costs.


New federal fuel efficiency and greenhouse gas emission standards for passenger cars and light trucks were established in 2010, applying to the 2012-2016 model years, replacing fuel efficiency standards for passenger vehicles that had been established decades earlier. In 2011, for the first time, new standards for fuel consumption and greenhouse gas emission were established for three classes of heavy duty vehicles:

  • Combination tractors ("semis")
  • Heavy-duty pickup trucks and vans
  • "Vocational vehicles", special purpose vehicles such as delivery trucks, buses, emergency vehicles, and motor homes.

In 2016, the standards were extended to trailers.

The Phase 1 and Phase 2 standards applying to each of these classes are summarized below. Note that the standards are expressed in terms of fuel consumption rather than fuel economy (as in "gallons per mile" instead of the more familiar "miles per gallon"). Different units are used for different classes of vehicles. Heavy-duty pickups and vans must meet gallon per mile standards (the same combination of units as for passenger vehicles, although expressed upside-down). The other classes, combination tractors and vocational vehicles, must meet gallon per ton-mile standards. This combination of units gives credit for pulling more weight, as well as for traveling a greater distance, on a given amount of gas (since you divide by a larger number in either case). To avoid having to deal with small fractions, the numbers are expressed in slightly modified units, gallons per ton per thousand miles, which multiplies the gallon per ton-mile values by 1,000.

The new standards are somewhat different from previous federal standards applying to trucks. The older standards regulate emissions of pollutants such as nitrogen oxides and smoke particles. It is primarily the engine that determines the level of these pollutants - the rest of the vehicle has comparatively little effect. Those standards accordingly applied most directly to engine manufacturers.

The quantities regulated by the new standards, fuel consumption and greenhouse gas emission levels, also depend on the engine, but in addition they are strongly influenced by the properties of the rest of the vehicle, such as the aerodynamic resistance of the tractor-trailer combination, and the rolling resistance of the tires. For this reason, the new rules apply to manufacturers of vehicles (including those who purchase their engines from other companies) as well as engine manufacturers. Trailers were not covered under the previous standards, but are now included under the Phase 2 standards.

1. Combination tractors

The standards apply to Class 7 and 8 combination tractors, vehicles whose gross vehicle weight rating, or GVWR (their fully loaded weight), exceeds 26,000 pounds. Trucks within this category are further classified according to their roof height, and whether or not they are sleeper cabs. Different standards apply in each case (see box).

The Phase 1 standards for fuel consumption and greenhouse gas emissions applied to the 2017 model year. The new Phase 2 standards apply in stages to the 2021, 2024, and 2027 model years. The following table lists the Phase 1 (2017) and Phase 2 (2027) standards for fuel consumption and greenhouse gas emissions for class 7 and 8 tractors:

(2017) and 2027 standards for combination tractors

(2017) and 2027 Model Year
(Gallons of Fuel per 1,000 Ton-Mile)

(2017) and 2027 Model Year GHG emissions (Grams CO2 per Ton-Mile)

Low Roof

Mid Roof

High Roof

Low Roof

Mid Roof

High Roof

Day Cab, Class 7







Day Cab, Class 8







Sleeper Cab, Class 8







(In addition to the Phase 1 categories, Phase 2 recognizes a class of vehicles designated "heavy-haul", having a Gross Combined Weight Rating exceeding 120,000 lb.)

(See Table III-1 in the final rule, page 98 of the PDF.)

Trucks designed for pulling flatbeds are generally designed with a low roof, while trucks designed for pulling box trailers are designed with higher roofs, to match the profiles of the load for better aerodynamics. In general, the standard is less stringent (poorer allowed fuel economy, and higher allowed emissions per mile per ton) for heavier trucks with high roofs, and for trucks with sleeper cabs, as compared to lighter and lower trucks. One reason is to remove any incentive for manufacturers to pass the standard with low-roof cabs that are then used to pull tall box trailers, a lose-lose situation for both operators and fuel economy.

2. Trailers

Trailers can have a significant effect on fuel efficiency, but setting standards for trailers poses significant problems. Trailers come in a wide variety of shapes and sizes, with many different constraints imposed by their various uses. The Phase 1 standards did not include trailers.

In Phase 2, through a collaboration of federal and state agencies, industry, and public interest groups, a reasonably consistent set of standards has been developed, covering a large fraction of the equipment currently on the road. The standards are to be applied in stages over a ten year period, and will apply fully starting with the 2027 model year and beyond.

For trailer manufacturers who are unfamiliar with the certification process, slides from an EPA workshop held on November 16, 2016 provide a detailed overview of the Phase 2 rule as it applies to trailers. Manufacturers must:

  • register with the EPA reporting system
  • collect input data for each family of trailers in commerce (the rules permit averaging over similar vehicle types)
  • calculate the expected emissions from each family, using a specified calculation method
  • assuming the calculated emissions are within the limit for the model year, submit the data and obtain certification
  • report actual production volumes for vehicles in each family at the end of the model year

In addition to complying with the recordkeeping and reporting aspects of the Phase 2 requirements, trailer manufacturers will have to decide how best to improve their vehicles to continue to meet the standards as emission limits tighten over the next ten years. Making trailers more fuel efficient involves several tradeoffs. Some key considerations, and a word of caution concerning emission calculation methods that apply specifically to box vans, are outlined below.


Although there are many types of trailers, their effects on fuel efficiency boil down to three main factors: the total weight (trailer itself plus load), aerodynamic resistance (at high speeds), and rolling resistance (at all speeds). Air resistance can be minimized by streamlining the flow of air past the trailer, adding fairings if necessary to fill gaps and smooth outer surfaces. Rolling resistance comes mainly from the tires, and depends both on the quality of the tires and on how well tire pressure is maintained. The standard aims at keeping both resistances as low as possible.

There is one unavoidable complication. Air resistance depends almost entirely on the outer shape of the trailer and the speed, and not on how much weight the trailer is carrying. Rolling resistance, on the other hand, is virtually independent of shape, and depends only modestly on the speed of the vehicle, but depends strongly on the weight of the load. Adding fairings can improve air resistance dramatically, but any added weight is bound to increase rolling resistance. Trailer manufacturers must therefore balance all three factors (weight, drag, and tire quality) to reduce the net resistance force, while staying within limits imposed by safety and cost constraints.

The Phase 2 rules require that trailer manufacturers obtain values for drag, weight, and rolling resistance for each of their products, and to use a model provided by EPA to calculate the fuel economy and emissions associated with those values. Similar (though more complicated) requirements already applied to engine and tractor manufacturers in Phase 1, and continue to apply in Phase 2. To demonstrate compliance with the tractor standards, engine and tractor manufacturers use a specific modeling tool (the Greenhouse Gas Emissions Model, or GEM) provided by EPA. GEM accepts input values specifying a wide range of characteristics of the engine or tractor being evaluated, and calculates an expected greenhouse gas emission rate (in grams of carbon dioxide equivalent per mile per ton of total load) over an appropriate drive cycle.

Trailer manufacturers may also choose to use GEM to demonstrate compliance. However, the regulation provides an alternative method for demonstrating compliance for standard box vans, the compliance equation, that provides approximately the same results as the GEM model, but is considered easier to use. To use the alternative method, the manufacturer multiplies each of the input values (drag, weight, and rolling resistance) by a numerical coefficient specified in the rule, and the results are added together to provide an estimated emission. The method gives results which agree with the GEM model to within a few percent.

The Phase 2 rules allow trailer manufacturers to use either the full GEM model or the method based on the compliance equation to demonstrate compliance. However, it may be worth noting that the small difference between the two methods, which may be considered too small to matter when setting emission standards, can lead to two different conclusions when optimizing designs for fuel economy. For example, a designer may have a fixed budget to improve the fuel economy of a box van, and can choose how much of it to spend on lightweight materials, and how much on lower rolling resistance tires. In calculating which combination of weight reduction and tire quality offers the best bang (or, in this case, best fuel economy) for the buck, it turns out that calculating expected emissions using the GEM model, versus using the compliance equation, can lead to significantly different results. When comparing alternative designs and optimizing choices within a set of constraints, the designer should use a model, like GEM, that includes the interplay between weight and rolling resistance, rather than the estimate provided by the compliance equation, which does not. See this document for a more detailed comparison of the two methods.

3. Heavy duty pickup trucks and vans

Standards for Class 2b and 3 vehicles (with fully loaded weight between 8500 and 14,000 pounds) are similar to those used for passenger vehicles, with a few exceptions that take into account the way the vehicles are used. The vehicles are tested under load in a standard driving cycle, as with passenger vehicles, but a "work factor" is applied that takes into account the vehicle's payload and its towing capacity. Four-wheel drive vehicles are also allowed somewhat more leeway. The Phase 2 standards lower allowable emissions by 2.5% per year from 2021 to 2027, and are expected to save 16% in fuel consumption beyond the level already attained in Phase 1.

4. Vocational vehicles

This category covers a wide variety of vehicle types, in weight classes spanning 2b through 8. They tend to be operated at lower speeds, so that improvements in aerodynamic resistance are generally less effective than improvements in rolling resistance. The standards, which are to be lowered in 2024 and again in 2027, are directed toward encouraging improvements in engine efficiency and toward the use of tires with less rolling resistance. (Low rolling resistance tires, becoming more common for combination tractors, are still relatively rare for vocational vehicles.)

Compliance Options

Compliance with the proposed heavy duty truck regulations will be largely the responsibility of vehicle and equipment manufacturers.

However, heavy duty vehicles typically remain in service for decades. Regulations which are unanticipated now might well be enacted during the service life of vehicles being purchased today that could impose requirements on vehicle operators as well as manufacturers. Such regulations could eventually include inspection requirements, or restrictions on vehicle operations. The details are impossible to predict, but as a general rule, whatever regulations are finally put in place will penalize less fuel efficient vehicles at the expense of more efficient ones. Put another way, the relative advantage of a more fuel efficient vehicle will become even more advantageous as rules are phased in. The net effect will be to shorten the payback time for investments in more fuel-efficient technology.

Aerodynamics becomes more and more important as speed increases. A ten percent increase in speed results in an over twenty percent increase in drag (and a correspondingly oversized loss in fuel economy). That's because nature charges two different penalties for speed - the vehicle has to push harder on the air to move through it faster, and the vehicle has to push more air out of the way at a time. The second factor is more significant than it might appear. A typical combination tractor traveling at 60 MPH has to push aside over 16 tons of air every minute.

Adding equipment to improve aerodynamics, such as fairings and wheel well covers, involves a tradeoff between extra fuel costs from the extra weight of the equipment and the fuel savings from reduced drag. Both costs and savings increase as speed increases, but the savings increase faster than the costs. (Extra vehicle weight results in more friction, which increases in proportion to speed. But extra aerodynamic drag, because of the double penalty, increases in proportion to speed squared.) So trucks that spend a lot of time at highway speeds are most likely to see significant reductions in fuel costs - and lower GHG emissions - from aerodynamic retrofits.

Best Practices

Best Practices for Improving Fuel Efficiency (Road Transportation)

The proposed regulations are primarily directed toward manufacturers rather than operators, and are intended to improve the performance of future vehicles. But operators can also take steps to improve fuel efficiency and reduce GHG emissions from existing vehicles.

Two of the most effective ways are to:

  • Improve aerodynamic flow, to reduce wind resistance
  • Use tires designed to reduce rolling resistance

In addition to equipment upgrades, operators can realize fuel economy and greenhouse gas emission reduction through operating practices. The EPA SmartWay program provides estimates of the cost savings and emissions reductions that can be realized through measures including:

  • Reducing idling time
  • Optimizing logistics
  • Moderating speed
  • Keeping tires inflated
  • Training drivers in fuel saving driving techniques

EPA Resources

Text of final Phase 2 rule

Regulatory Impact Analysis