The Advanced Light-Duty Powertrain and Hybrid Analysis tool was created by Environmental Protection Agency to evaluate the greenhouse gas emissions and fuel efficiency of light-duty vehicles. It is a physics-based, forward-looking, full vehicle computer simulator that is capable of analyzing various vehicle types equipped with different powertrain technologies. The software is built on MATLAB/Simulink. This first version release of the simulation tool models conventional vehicles and is capable of evaluating effects of off-cycle technologies on greenhouse gas emissions, such as air conditioning, electrical load reduction, road load reduction by active aerodynamics, and engine start-stop.This paper introduces the simulation tool by describing its basic model architecture and presenting its underlying physics as well as model formulations. It describes the simulation capability along with its graphical user interface of the tool, designed for off-cycle technology analysis purposes. Model validation results are provided by comparing the simulation outputs with conventional production vehicle test data. The paper concludes with a description of the role this model played in determining the effects of off-cycle technologies on greenhouse gas emissions to support development of the off-cycle credits finalized in the recent Greenhouse Gas Emissions and Fuel Economy rule.