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