VARIABLE ERRORS SET A LIMIT TO ADAPTATION. Paper presented at: Errors in the Operation of Transport Systems : proceedings of a CEC Workshop held at the Medical Research Council's Applied Psychology Unit, Cambridge, UK, May 26-28, 1989.

This paper argues that variable error introduces a limit to the extent to which a person can be adapted to his or her environment in general, and for the extent to which the driver can be adapted to the traffic environment in particular. This is because variable error turns what is a deterministic and stable world into an uncertain one where it is only possible to be adapted in a statistical sense. A series of experiments are then discussed. These experiments show that drivers match their utilization of perceptual information to the validity of this information, ie they treat uncertainty introduced by variable error in the perceptual system in the same manner as they treat uncertainty in the physical system. This supports the main hypothesis of the paper. A driver may mitigate the effects of variable error by having a safety margin, but the relation between speeds and accident rates (predicted from the current hypothesis) shows that this adaptation is not effective enough. Safety authorities may mitigate the effects of variable error by decreasing the variability of the driving environment, eg by introducing speed limits. (A) For the covering abstract of this conference see IRRD 834497.