A sample of 1006 professional truck drivers were surveyed on their perceptions of self and average other speeds, consideration, relative safety, and relative skill. A disproportionate frequency of responses is found in the measures of speed, safety, and consideration, but not skill. In the measures of speed and consideration this bias is found to operate in a negative direction. Truck drivers are found to evaluate other road users negatively, they do not demonstrate 'self-enhancement' indicative of driver overconfidence. Drivers responsible for the biases are isolated from the sample using a method of triangulation. Background factors relating to driver characteristics and employment conditions are examined. Characteristics of the drivers' employment indicate the perceptions are related to factors external to the drivers' self-conceptions. These contrasts provide further support for the contention that the 'self-enhancement bias', as it appears in this sample, operates as a negative-other rationalisation.