Abstract
The nature of air ions is discussed and their natural and artificial production described. Evidence of their biological and psychological effects is presented. Special attention is given to assessment of reported findings of air ion effects on reaction time, affect, sensation, and other functions of possible significance in driving behaviour. The production of air ions by the motor vehicle through heat radiation and through exhaust gases is discussed, with additional consideration of traffic congestion and regional (geographic) characteristics which may contribute to air ion conditions. A systematic theory is developed for testing specific air ion effects on driving behaviour.