Gössling et al. (2023) perform a Cost-Benefit Analysis (CBA) of a 130 kph speed limit on German highways (Autobahnen). They find that the social benefits of the policy significantly outweigh its social costs, generating a welfare gain of almost €1 billion annually. In this commentary, we point to several serious shortcomings in their analysis, mainly caused by disregarding fundamental principles of economic CBA and adopting misleading ad hoc assumptions. We conclude that their CBA is neither suitable nor sufficient to evaluate the economic efficiency of a speed limit policy in Germany.