To determine the level of adherence by transport cyclists to road rules in traffic situations and their reasons for non-adherence.The Safer Cycling Study was a prospective cohort study of transport and recreational cyclists. Over 2000 cyclists were recruited between March and November 2011.770 Transport cyclists aged 18 years and older, who lived in New South Wales, Australia. Participants completed a baseline questionnaire plus provided data during a further six survey weeks over 12 months. In one of their survey weeks, cyclists were asked how often they infringed road rules and what contributory factors led to their road rule infringement. Data were collected via web-based online questionnaires.Quantitative data were analysed descriptively. Qualitative data were analysed to identify themes derived from the text.Riding on the footpath and red light infringement were the most commonly reported road rule breaches. Poor infrastructure design was the most frequently identified contributing factor to road rule breaches, followed by the speed of motorised traffic and the behaviour of other road users.A transport network needs to facilitate cyclists of all capabilities to reach their required destination in a safe and timely manner, and encourage compliance with the road rules.