The Environmental Protection Agency’s (EPA’s) Advanced Light-Duty Powertrain and Hybrid Analysis (ALPHA) tool was created to estimate greenhouse gas (GHG) emissions from light-duty vehicles. ALPHA is a physics-based, forward-looking, full vehicle computer simulation capable of analyzing various vehicle types with different powertrain technologies, showing realistic vehicle behavior, and auditing of all internal energy flows in the model. The software tool is a MATLAB/Simulink based desktop application. In preparation for the midterm evaluation of the light-duty GHG emission standards for model years 2022-2025, EPA is refining and revalidating ALPHA using newly acquired data from model year 2013-2015 engines and vehicles. From its database of engine and vehicle benchmarking data EPA identified the most efficient, engines, transmissions and vehicle technologies, and then used ALPHA to model a midsized car incorporating combinations of these existing technologies which minimize GHG emissions. In a similar analysis, ALPHA was used to estimate the GHG emissions from future low-GHG technology packages potentially available in model year 2025. This paper presents the ALPHA model inputs, results and the lessons learned during this modeling and assessment activity.