Despite the aggressive enforcement of speed limits, speeding remains the second leading cause of fatalities in vehicle accidents in South Africa. Speeding fines are one mechanism for enforcing speed limits; however, these are only effective deterrents against speeding if fines are enforced. The potential effectiveness of speeding fines to increase safety on South African roads is rendered almost obsolete because so many offenders default on payment. Our aim was to utilise the Theory of Planned Behaviour as a framework to explore motorists’ perceptions of factors that may influence the payment of speeding fines in Cape Town, South Africa. Self-report data were collected from participants who had received fines ( n = 268), about their speed fine-paying behaviour, their perceptions of the consequences of non-payment, subjective and social norms, and control beliefs about the ease with which fines can be paid and motorists’ ability to afford fines. Regression analysis showed that motorists who report paying their fines are more likely than those who do not pay to hold beliefs that non-payment will result in serious consequences, affirm injunctive norms supporting the payment of fines, believe that it is easy to pay fines, and are able to afford to pay. This study provides novel insights into the potential of theories of behaviour change to design evidence-based behavioural interventions to encourage motorists to comply with speeding fines and hence to improve road safety in South Africa.