Traffic accidents on roads are a major global contributor to fatalities. Numerous elements contribute to these accidents, including demographic factors, human behavior, road infrastructure, and environmental conditions. Variations in the external environment can alter driving capabilities, and among these variables, weather conditions like fog, rain, and snow stand out as significant factors impacting driving performance. This paper investigates the adverse weather impact on driver performance and cognitive state assessment in three-wheeler drivers. The main objective of this study is to investigate how adverse weather affects drivers’ cognitive performance and states, such as mental workload, attention, and fatigue. The experiment involved 45 licensed three-wheeler drivers using a fixed driving simulator at the Ergonomics Laboratory of the Indian Institute of Management, Mumbai. The cognitive states of the participants were evaluated using the QUASAR cognitive state classification gauge (Q-States) and a DSI-7 dry electrode EEG headset under varying environmental and traffic conditions. The study revealed significant differences in drivers’ mental workload, attention, and drowsiness levels in challenging weather and traffic scenarios.