With the increasing number of road traffic deaths, transportation safety-related study has gained a significant amount of research interest. Tri-axial acceleration values and vehicle speed are observed to be the most efficient vehicular features to identify and measure unsafe driving events. An abnormality index has been proposed to quantify the extent of driving anomaly. The effects of different external stimuli, such as auditory, olfactory, and visual stimuli, over the proposed abnormality index have been studied, and the index is further validated by a set of experimental data collected from a total of 70 sessions of real-time driving experiments. These results can be incorporated further for developing better driving safety systems to cause the advancement of existing autonomous vehicles.