2 Abstract: Driving is a daily activity throughout the world. However, driving at highways or city requires significant cognitive and motor skills such as visual-spatial ability, memory and information processing and rapid reaction. Recent studies show lack of driver alertness to be a major cause of automobile accidents on roadways across the world. The perceived state of alertness is a complex physiological and psychological phenomenon. This paper reviews factors contributing to and the symptoms of alertness and the existing methods used to measure driver alertness.