In the current transport policy debate on inner-city pollution levels and speed limits on motorways, it is common that advocates and opponents of certain measures exchange arguments that completely lack evidence-based, reliable and verifiable data. This widens the gap between the yes and no sides and does little to further the political debate. Two aspects are particularly striking in the overall debate: Firstly, decision-makers have failed to communicate to interested members of the public how empirical evidence is used to address this issue, and in particular, how a causal relationship between a planned measure (e.g. speed limit) and a variable (e.g. accident figures) can be identified conclusively. Secondly, this sometimes heated debate tends to be limited to a few dimensions, which prevents a comprehensive assessment and consideration of the social costs and benefits of potential measures. This ZEW policy brief recommends approaching causal relations in a more careful and differentiated way when assessing measures and threshold values, taking into account indicators that are relevant from a social point of view.