Starting January 2022 all light passenger and commercial road vehicles sold in Brazil will need to comply with PROCONVE L7 (PL7) emissions regulation. PL7 requirements consists in more stringent emissions limits and new procedures must be performed, being Real Driving Emissions (RDE) one of them. The RDE test will analyze all the main pollutants, such as THC, CO, NOx and CO2, emitted by vehicles while driven on public roads and over a wide range of different conditions (altitude, ambient temperature, vehicle payload, grades, traffic and vehicle speeds). The definition of routes that can be used for the RDE tests is a challenge because it needs to handle all the external factors while complying with regulation constraints. The purpose of this study is to develop a new methodology to validate different RDE routes in the absence of the Portable Emissions Measurement System (PEMS), which is a very expensive equipment to acquire and operate. To achieve this goal, a Carbon Dioxide (CO2) model was designed based on data from the Engine Control Unit (ECU). This simplified approach provides the following benefits: cost reduction since no dedicated PEMS for routes definition is needed; and timing reduction, given PEMS installation and debug is avoided. Applying this method, the engineering team will be able to make faster and lower cost iterations for different powerpacks, power/weight ratios and driver styles, which is crucial to define robust RDE routes for final vehicles sign-off. The European RDE requirements are used as reference for this study. The main results and model validation will be detailed on this paper.