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National Research Council Report Explores Improving Fuel Economy of Medium- and Heavy-Duty Vehicles; Recommends Immediately Beginning Developing a Regulatory Approach

Comparison of 2015-2020 new vehicle potential fuel-saving technologies for seven vehicle types: tractor trailer (TT), Class 3-6 box (box), Class 3-6 bucket (bucket), Class 8 refuse (refuse), transit bus (bus), motor coach (coach), and Class 2b pickups and vans (2b). Source: TIAX. Click to enlarge.

The National Research Council has released a prepublication edition of a new congressionally mandated report that evaluates various technologies and methods that could improve the fuel economy of medium- and heavy-duty vehicles (MHDVs), such as tractor-trailers, transit buses, and work trucks.

The report also recommends approaches that federal agencies could use to regulate these vehicles’ fuel consumption. Currently there are no fuel consumption standards for such vehicles, which account for about 26% of the transportation fuel used in the US. The report finds that there is an immediate need to begin the development of such a regulatory approach.

Significant engineering work will needed to produce an approach that results in fuel efficiency standards that are cost effective and that accurately represent the effects of fuel consumption reducing technologies. The regulations should fit into the engineering and development cycle of the industry and provide meaningful data to vehicle purchasers, the report says.

The report does not recommend a specific numerical standard. Instead, the National Highway Traffic Safety Administration (NHTSA)—the agency is charge of CAFE—should establish fuel consumption metrics tied to the task associated with a particular type of MHDV and set targets based on potential improvements in vehicle efficiency and vehicle or trailer changes to increase cargo carrying capacity, the report recommends.

The miles-per-gallon measure used to regulate the fuel economy of passenger cars is not appropriate for medium- and heavy-duty vehicles, which are designed above all to carry loads efficiently, the report notes. Instead, any regulation of medium- and heavy-duty vehicles should use a metric that reflects the efficiency with which a vehicle moves goods or passengers, such as gallons per ton-mile, a unit that reflects the amount of fuel a vehicle would use to carry a ton of goods one mile. This is called load-specific fuel consumption (LSFC).

NHTSA should determine whether a system of standards for full but lightly loaded (cubed-out) vehicles can be developed using only the LSFC metric or whether these vehicles need a different metric to properly measure fuel efficiency without compromising the design of the vehicles, the report suggests.

The committee estimated the improvements that various technologies could achieve over the next decade in seven vehicle types. For example, using advanced diesel engines in tractor-trailers could lower their fuel consumption by up to 20% by 2020, and improved aerodynamics could yield an 11% reduction. Hybrid powertrains could lower the fuel consumption of vehicles that stop frequently, such as garbage trucks and transit buses, by as much as 35% in the same time frame.

While the cost of making these improvements would be passed on to vehicle purchasers, the report notes that many of these suites of technologies would pay for themselves even at today’s energy prices, under the committee’s assumptions.

The report also estimates the costs and maximum fuel savings that could be achieved for each type of vehicle by 2020 if a combination of technologies were used. The best cost-benefit ratio was offered by tractor-trailers, whose fuel use could be cut by about 50% for about $84,600 per truck; the improvements would be cost-effective over ten years provided gas prices are at least $1.10 per gallon.

The fuel use of motor coaches could be lowered by 32% for an estimated $36,350 per bus, which would be cost-effective if the price of fuel is $1.70 per gallon or higher. For other vehicle classes, the financial investments in making improvements would be cost-effective at higher prices of fuel.

Among the major findings from the study are:

  • While it may seem expedient to initially focus on those classes of vehicles with the largest fuel consumption (i.e., Class 8, Class 6, and Class 2b, which together account for approximately 90 percent of fuel consumption of MHDVs), selectively regulating only certain vehicle classes would lead to very serious unintended consequences and would compromise the intent of the regulation. Within vehicle classes, there may be certain subclasses of vehicles (e.g., fire trucks) that could be exempt from the regulation without creating market distortions.

  • Large OEMs, with significant engineering capability, design and manufacture almost all Class 2b, 3, and 8b vehicles. Small companies with limited engineering resources make a significant percentage of vehicles in Classes 4 through 8a, although in many cases they buy the complete chassis from larger OEMs. Regulators will need to take the limitations of these smaller companies into account.

  • Commercial trailers are produced by a separate group of manufacturers that are not associated with truck manufacturers. Trailers, an important opportunity for fuel consumption reduction, can benefit from improvements in aerodynamics and tires.

  • Using the process and results from existing engine dynamometer testing for criteria emissions to certify fuel economy standards for MHDVs would build on proven accurate and repeatable methods and put less additional administrative burden on the industry. However, to account for the fuel consumption benefits of hybrid powertrains and transmission technology, the present engine-only tests for emissions certification will need to be augmented with other powertrain components added to the engine test cell, either as real hardware or simulated components. Similarly, the vehicle attributes (aero, tires, mass) will need to be accounted for, one approach being to use vehicle-specific prescribed loads (via models) in the test cycle. This will require close cooperation among component manufacturers and vehicle manufacturers.

Specific major recommendations of the report include:

  • When NHTSA regulates, it should regulate the final-stage vehicle manufacturers since they have the greatest control over the design of the vehicle and its major subsystems that affect fuel consumption. Component manufacturers will have to provide consistent component performance data. As the components are generally tested at this time, there is a need for standardized test protocol and safe guards for the confidentiality of the data and information. It may be necessary for the vehicle manufacturers to provide the same level of data to the tier suppliers of the engines, transmissions, after-treatment and hybrid systems.

  • Simulation modeling should be used with component test data and additional tested inputs from powertrain tests, which could lower the cost and administrative burden yet achieve the needed accuracy of results. This is similar to the approach taken by Japan, but with the important clarification that the program would represent all the parameters of the vehicle (powertrain, aerodynamics, and tires) and relate fuel consumption to the vehicle task.

  • Congress should appropriate money and NHTSA should implement as soon as possible a major engineering contract that would take several actual vehicles covering several applications and develop the approach to component testing data in conjunction with vehicle simulation modeling to arrive at LSFC data for these vehicles. The actual vehicles should also be tested by appropriate full-scale test procedures to confirm the actual LSFC values and the reductions measured with fuel consumption reduction technologies in order to validate the evaluation method.

  • NHTSA should conduct a pilot program to “test drive” the certification process and validate the regulatory instrument proof of concept.

While regulating medium- and heavy-duty vehicles will be more complicated than it is for passenger cars because of the variety of vehicles and their differing tasks and terrains, the barriers are not insurmountable, the report finds. Japan regulates the fuel economy of these vehicles, and both the European Union and the state of California are developing standards.

However, one way to avoid the complexity of regulating different types of vehicles would be to impose a fuel tax, which would induce firms to optimize the fuel-efficiency of their operations. The report urges Congress to consider this approach. Another alternative approach—applying a cap-and-trade system to trucking companies similar to the one that Congress is considering as a way to lower CO2 emissions—would similarly provide these companies with an incentive to adopt fuel-saving technologies and operational methods.

In addition, the report recommends nontechnical methods NHTSA could use to lower fuel consumption, including providing incentives to train vehicle operators in efficient driving techniques, which can result in fuel savings of anywhere from 2-17%. One approach could be to establish a process to train and certify drivers in these techniques as part of commercial driver license certification.

In 2007 Congress passed legislation requiring the US Department of Transportation to establish the first fuel economy standards for medium- and heavy-duty vehicles. The National Highway Traffic Safety Administration asked the National Research Council to recommend the best ways to measure and regulate fuel economy for these vehicles, and assess technologies that could improve it.

The study was sponsored by the National Highway Traffic Safety Administration. The National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council make up the National Academies. They are private, nonprofit institutions that provide science, technology, and health policy advice under a congressional charter. The Research Council is the principal operating agency of the National Academy of Sciences and the National Academy of Engineering.



Henry Gibson

Reducing the speed limit for these vehicles can gain vast improvements.

Putting more container freight and more piggyback trailer freight on the railroads with higher fuel taxes on trailer trucks can also increase the fuel efficiency dramatically.

The use of the Artemis, Noax or other hydraulic hybrid systems for any or all of these vehicles can reduce fuel consumption greatly at much lower costs than electrodynamic systems.

High volume mass production of Capstone diesel turbines and hybrid electric drive with ZEBRA or GE nickel-sodium batteries can also cut the cost of operation and repairs and maintenance sufficient for a short payback. Trucks and tractors are large enough to build in turbines with combined Rankine cycles to recover waste heat. Such facilities would take far less room than a sleeper cab and there is now no practical limit on the length of the truck. Two or three turbines will allow only as many as are needed to be operated for high efficiency, but there are even forgotten techniques to allow highly efficient operation of turbines at part load. The issue is of little concern with the addition of nickel-sodium batteries that can have higher practical capacity and life than most or all lithium batteries in production.

New buses and tractor trailers should be equipped with sensors for recording the efficiencies of such operation moment by moment. This is possible with USB devices for 10 dollars for 4 giabytes and one dollar microcontrollers. GE already proved the more efficient operation of hybrid elecrtric locomotives and trucks.


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