<p>Speeding behaviour is often linked to risk-taking and significantly increases the propensity for crashes. It becomes even more critical during extreme weather conditions, such as rainfall, and in mountainous regions. Moreover, understanding the determinants of speeding behaviour in a low- and middle-income country like India is essential. This study investigates the key psychological predictors of speeding intentions and behaviour among car drivers and motorbike riders in India during rainy weather in mountainous regions, using an extended version of the Theory of Planned Behaviour (TPB). A total of 600 responses were collected through a user-perception survey, 300 each for car drivers and motorbike riders. Hierarchical regression analysis was conducted to model the influence of TPB variables (attitudes, subjective norms, and perceived behavioural control) and extension variables (moral norms, risk perception, and fatalistic beliefs) on the intention to violate speed limits and speeding behaviour. Attitudes towards speeding were found to have the strongest impact on intentions to violate speed limits. Subjective norms showed a significant negative association with speeding behaviour, indicating that when family members or close relatives disapprove of drivers’ or riders’ speeding behaviour, individuals are less likely to speed. Overall, the extended TPB models successfully predicted 52.5% and 77.2% of the variance in speeding intentions, and 74.7% and 70.9% of the variance in speeding behaviour of car drivers and motorbike riders, respectively. The study findings may assist policymakers and road safety officials in better understanding the psychological factors underlying drivers’ and riders’ speeding behaviour.</p>