Abstract
This study examined psychological and psychical changes in one solo truck driver and both drivers in a two-up truck crew during several 5-6 day round-trips to the north west of Western Australia. Endocrine catecholamine levels, cardiac sinus arrhythmia and serial reaction performance all showed progressive changes over the journey. The solo driver showed greater changes on most measures than the two-up crew and compared with control measures obtained from research assistants accompanying the drivers. The results suggest that solo drivers may experience more fatigue, impaired capacity for controlled mental effort and slowed reactions than a two-up crew. (A)