A simulator and a field experiment were conducted to study the effects of visual and cognitive load on driving performance, and also to assess the validity on the VTI simulator as a tool for studying the effects of distraction. It was found that visual load resulted in deteriorated lateral control and to some extent reduced speed control, although there was a clear effect of the drivers reducing their speed and increasing the steering activity in order to compensate for the increased visual load. Cognitive load resulted in somewhat reduced speed control, but more clearly, increased steering activity and more stable lane keeping. This increase in lateral control was interpreted as the drivers in precaution creating a larger safety margin in case of an unexpected event, which they were assumed to be less capable to react to due to the cognitive load. The simulator validity was found to be very high, except from that less realistic risk in the simulator seemed to result in less level of stress and higher travel speed in the simulator.