A Detailed Vehicle Simulation Process to Support CAFE Standards for the MY 2024–2026 Analysis

Abstract

In 1975, Congress passed the Energy Policy and Conservation Act (EPCA), requiring standards for corporate average fuel economy (CAFE), and charging the U.S. Department of Transportation (DOT) with the establishment and enforcement of these standards. The Secretary of Transportation has delegated these responsibilities to the National Highway Traffic Safety Administration (NHTSA). NHTSA has contracted the DOT Volpe National Transportation Systems Center (Volpe Center) to provide analytical support for NHTSA’s regulatory and analytical activities related to fuel economy standards. Unlike long-standing safety and criteria pollutant emissions standards, fuel economy standards apply to manufacturers’ overall fleets rather than to individual vehicle models. In developing the standards, NHTSA made use of the CAFE Compliance and Effects Modeling System (the CAFE model), which was developed by DOT’s Volpe Center for the 2005–2007 CAFE rulemaking and has been continually updated since. The model is the primary tool used by the agency to evaluate potential CAFÉ stringency levels by applying technologies incrementally to each manufacturer’s fleet until the requirements under consideration are met. The CAFE model relies on numerous technology-related and economic inputs, such as market forecasts and technology cost and effectiveness estimates. These inputs are categorized by vehicle classification, technology synergies, phase-in rates, cost learning curve adjustments, and technology decision trees. The Volpe Center assists NHTSA in the development of the engineering and economic inputs to the CAFE model by analyzing the application of potential technologies to the current automotive industry vehicle fleet to determine the feasibility of future CAFÉ standards, the associated costs, and the benefits of the standards. Part of the CAFE model’s function is to estimate CAFE improvements that a given manufacturer could achieve by applying additional technologies to specific vehicles in its product line. Because CAFÉ standards apply to the average fuel economy across manufacturers’ entire fleets of new passenger cars and light trucks, the model, when simulating manufacturers’ potential application of technology, considers the entire range of each manufacturer’s product line. This typically involves accounting for more than 1,000 distinct vehicle models and variants, many more than can be practically examined using full vehicle simulation (or the other techniques mentioned above). Instead, the model uses estimates of the effectiveness of specific technologies for a representative vehicle in each vehicle class, and arranges technologies in decision trees defining logical progressions from lower to higher levels of cost, complexity, development requirements, and/or implementation challenges. All inputs to CAFE’s decision tree model are related to the effectiveness (fuel consumption reduction) of each fuel-saving technology. Although vehicle testing could be used to estimate these factors, vehicle testing that spans many vehicle types and technology combinations could be prohibitively resource-intensive. Another alternative, either as a substitute for or as a complement to vehicle testing, is to make greater use of vehicle simulation. Full vehicle simulation tools use physics-based mathematical equations, engineering characteristics (e.g., engine maps, transmission shift points, hybrid vehicle control strategies), and explicit drive cycles to predict the effectiveness of individual fuel-saving technologies as well as their combinations. Argonne National Laboratory, a U.S. DOE national laboratory, has developed a full vehicle simulation tool, Autonomie, which has become one of the industry’s standard tools for analyzing vehicle performance, energy consumption, and technology effectiveness. Through an Inter Agency Agreement, the DOE Argonne Site Office and Argonne National Laboratory have been tasked with conducting full vehicle simulation t