The main purpose of this study is to measure the impact of environment factors of simulated road tunnels on driver performance. Perceptual cues in the tunnel environment are manipulated in order to evaluate performance measures and examine possible implications for road tunnel safety. The effects of environment factors on driver workload are obtained from 1) objective primary task performance measures (vehicle speed, lateral position, steering wheel reversal rate) and 2) a secondary task performance measure (peripheral detection task). By manipulating visual information it was expected that driver performance could be improved and that our understanding of the demands and needs of tunnel driving can also help us determine which ITS applications may be appropriate in tunnels. The main results suggest that the effects of different tunnel designs used in this study do not affect performance significantly. They also suggest that tunnel driving in general leads to compensatory behaviour due to increased effort. The present study does not, however, have enough evidence to suggest that it is safe to allow a multitude of ITS applications in tunnels. Additionally, the effects of drowsiness are clearly distinguishable in the primary and secondary task performance measures.