- The aim of this study was to investigate the relationships between subjective feeling, performance and physiological strain, while driving under the influence of two blood alcohol concentrations (BAC), 0.5 g/kg and 1.0 g/kg. Six male and six female students drove in a car simulator after drinking alcohol. All subjects reported that driving was difficult only at the high alcohol level. Four indicators of performance were used: ability to maintain lane position, Root mean square (RMS) of steering deviation RMS of linear speed and average speed. The ability to maintain lane position was affected by both levels of alcohol. RMS of steering deviation was impaired only by the high alcohol concentration, while the average speed and the RMS of speed were not affected at all. Alcohol increased heart rates (HR), but the driving task did not cause further increase compared to initial rest values. Heart rate variability (HRV) decreased significantly at high alcohol levels. Ratios of Beta/Alpha waves of the EEG spectra showed that subjects were sleepier while driving at the high alcohol concentration. These results indicate that more than one variable should be considered when the effects of alcohol intoxication are being quantified. Despite the drivers' feelings, which were affected only at the high level of alcohol, performance measures, such as lane position and physiological strain, were affected by both levels of alcohol. In summary, this study emphasizes the importance of using multiple measures of alcohol effects in order to understand their impact on mood and behavior. Background It is generally accepted that driving under alcohol intoxication, is a major cause of traffic accidents. Definition of intoxication levels however, varies among different countries. Based on data that showed impairment of driving skill due to increased alcohol blood levels, a range of tolerance between 1g/Kg to 0.5g/Kg is generally accepted. Although performance seems to be the primary variable of interest in assessing the effects of alcohol on traffic safety, other variables should also be considered when dealing with accident prevention. Two such variables are: subjective feelings and mental abilities reserves of the drivers. a: Subjective assessments of driving ability can be a crucial factor of road accidents. A disparity between the driver perceptions of his ability to the actual mental state can lead to inevitable accidents. b: Driver's mental stress or physiological strain.