This paper sets out by identifying five plausible stages in the automa
tion of the road traffic system, ranging from the introduction of part
systems that support specific task components (navigation, collision
avoidance) to full automation of roads and vehicles. It is then attemp
ted to predict how drivers will respond to each successive stage of au
tomation, and how this will, become manifest in driver behavior. On th
e basis of this the paper assesses the safety consequences of each sep
arate stage of automation.