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• There are no comprehensive pre-post evaluations of bicycle passing distance rules. • The Queensland passing distance rule had high levels of awareness and compliance. • Countermeasure implementation sometimes precedes understanding of causation. • Countermeasure evaluations can generate data useful to understand crash causation. Close passes by motor vehicles endanger both the safety and comfort of bicycle riders. Governments in many countries have introduced laws requiring drivers to maintain at least a minimum distance between their vehicle and the cyclist they are passing, despite relatively poor understanding of the causes of bicycle overtaking crashes at the time. Queensland was the first state in Australia to introduce such a law, with a two-year trial commencing in April 2014. The data collected during the evaluation of the trial were later analysed to answer two main questions: "Under what circumstances do close passes occur?" and "Why do drivers pass too close?". The first question was largely approached by analysing the video observations of more than 18,000 riders (including 2,000 passing events) at 15 locations on Queensland roads and examining the infrastructure, traffic and road user characteristics that influenced passing distances. The second question was addressed in experimental studies which used the video observations as stimuli. This paper demonstrates how the political need for evaluation of a countermeasure can act as a stimulus for research funding that then allows data collection, analysis and better understanding of crash causation. Logically, introduction of a countermeasure should be based on a rigorous understanding of crash causation. But when this does not occur, evaluation may provide data that can be used to answer questions about crash causation – or at least pose new questions. [ABSTRACT FROM AUTHOR]