address the duty cycles that characterize different types of vehicles and their wide range of applications.
The fundamental engineering metric for measuring the fuel efficiency of a vehicle is fuel consumption, the amount of fuel used, assuming some standard duty or driving cycle, to deliver a given transportation service, for example, the amount of fuel a vehicle needs to go a mile or the amount of fuel needed to transport a ton of goods a mile. For light-duty vehicles (cars and light trucks), the corporate average fuel economy (CAFE) program uses miles per gallon (mpg). This measure, although derived from measurements of fuel consumption in gallons/mile, is not the appropriate measure for MHDVs, since these vehicles are designed to carry loads in an efficient and timely manner. A partially loaded tractor trailer would consume less fuel per mile than a fully loaded truck, but this would not be an accurate measure of the fuel efficiency of moving goods. However, normalizing fuel consumption by the payload and using the calculation of gallon/ton-mile—the load-specific fuel consumption (LSFC)—the fully loaded truck would have a much lower LSFC number than the partially loaded truck, reflecting the ability of the truck to accomplish the task of delivering goods.
Finding 2-1. Fuel consumption (fuel used per distance traveled; e.g., gallons per mile) has been shown to be the fundamental metric to properly judge fuel efficiency improvements from both engineering and regulatory viewpoints, including yearly fuel savings for different technology vehicles.
Finding 2-2. The relationship between the percent improvement in fuel economy (FE) and the percent reduction in fuel consumption (FC) is nonlinear; e.g., a 10 percent increase in FE (miles per gallon) corresponds to a 9.1 percent decrease in FC, whereas a 100 percent increase in FE corresponds to a 50 percent decrease in FC. This nonlinearity leads to widespread consumer confusion as to the fuel-savings potential of the various technologies, especially at low absolute values of FE.
Finding 2-3. MHDVs are designed as load-carrying vehicles, and consequently their most meaningful metric of fuel efficiency will be in relation to the work performed, such as fuel consumption per unit payload carried, which is load-specific fuel consumption (LSFC). Methods to increase payload may be combined with technology to reduce fuel consumption to improve LSFC. Future standards might require different values to accurately reflect the applications of the various vehicle classes (e.g., buses, utility, line haul, pickup, and delivery).
Recommendation 2-1. Any regulation of medium- and heavy-duty vehicle fuel consumption should use LSFC as the metric and be based on using an average (or typical) payload based on national data representative of the classes and duty cycle of the vehicle. Standards might require different values of LSFC due to the various functions of the vehicle classes e.g., buses, utility, line haul, pickup, and delivery. Regulators need to use a common procedure to develop baseline LSFC data for various applications, to determine if separate standards are required for different vehicles that have a common function. Any data reporting or labeling should state an LSFC value at specified tons of payload.
Although a CAFE regulatory program has been implemented for light-duty vehicles, where the responsibility for the manufacture and certification of vehicles is well defined and the configurations of cars and light trucks for sale are well defined and of limited number, the MHDV world is much more complicated. There are literally thousands of different configurations for vehicles, including bucket trucks, pickup trucks, garbage trucks, delivery vehicles, and long-haul tractor trailers. Their duty cycles vary greatly. Some stop and go every few seconds; others spend most of their time at highway speeds. Furthermore, the party responsible for the final truck configuration is often not well defined. For example, a body builder (vehicle integrator) may be the manufacturer of record, but the body builder may not design or even specify the chassis and power train. For tractor-trailer combinations, the tractor and trailer are always made and often owned by different companies, and a given tractor may pull hundreds of different trailers of different configurations over its life. Many trucks are custom made, literally one of a kind.
Even though the regulation of such vehicles will be much more complicated than it is for light-duty vehicles, the barriers are not insurmountable. Safety and emission regulations have been implemented, and regulations for fuel consumption in medium- and heavy-duty trucks already exist in Japan and are under development by the European Commission. California is building on the EPA’s SmartWay Partnership to implement its own approach to regulating truck fuel consumption.
Finding 3-1. Although it took years of development and substantial effort, regulators have dealt effectively with the diversity and complexity of the vehicle industry for current laws on fuel consumption and emissions for light-duty vehicles. Engine-based certification procedures have been applied to address emissions from heavy-duty vehicles and the myriad of nontransportation engines.