Following its commitment to reduce CO2 emissions from road transport in Europe, the European Commission has launched the development of a new methodology for monitoring CO2 emissions from heavy-duty vehicles (HDV). Due to the diversity and particular characteristics of the HDV sector it was decided that the core of the proposed methodology will be based on a combination of component testing and vehicle simulation. A detailed methodology for the measurement of each individual vehicle component of relevance and a corresponding vehicle simulation is being elaborated in close collaboration with the European HDV manufacturers, component suppliers and other stakeholders. Similar approaches have been already adopted in other major HDV markets such as the US, Japan and China.In order to lay the foundations for the future HDV CO2 monitoring and certification software application, a new vehicle simulation software was developed, Vehicle Energy Consumption calculation Tool (henceforward VECTO). VECTO aims to serve as a platform that will incorporate the findings of current research activities in the field of HDV fuel consumption simulation and serve as a pilot for future upgrades and developments of the software application to be included in the European regulation. Emphasis was put from the very beginning on features that are of importance to HDV in order to reflect realistically both the actual vehicle CO2 emissions during operation and the competitive advantages of various fuel/CO2 saving technologies of the vehicles.This paper describes the simulation tool, its key characteristics and summarizes the most important future updates that are under investigation. In addition a first validation of its performance against real world measurement data is presented. The tool was also benchmarked against three widely available commercial vehicle simulators. Results suggest good ability to reproduce tests but further developments are still necessary in order to accurately reflect the real world fuel consumption of modern HDVs.