The Carbon Disclosure Project (CDP.net) which acts as a global repository for corporations who commit to responsibly measure their carbon footprint and then take steps to reduce it significantly, has the following reference to vehicle emission reporting:
“CDP makes no judgments on standards or methodologies applied by companies to produce their inventories. As such, it is impossible for CDP to explicitly accept/reject a specific calculation methodology. We expect that any tool used to calculate emissions for an inventory will follow the best practice and that it will adhere to good practice, and observe important aspects such as the accuracy and completeness principles of standards like the GHG Protocol. Any methodology needs to be evaluated for each specific case to understand if its application is appropriate, considering cost and the principles of GHG accounting. Thus, evaluating whether or not a certain practice is appropriate for a given purpose is best completed by verifiers/assurers. We expect companies that follow best practice to verify/assure their inventories, namely the methods used to estimate the emissions and the underlying data. Verifiers/assurers will have the necessary training and skills to establish if the methodologies used were the appropriate ones or not, for each case.”