Dependence of human adaptation and risk compensation on modification in level of automation for system safety

We examine the dependence of risk compensatory human adaptation to a system to attain safety of everyday machines, such as cars, on the level of automation and its shift. Two experiments were conducted using a microworld that is closely related to driving. The first experiment clarifies differences in the operation method and in risks involved in operation among different levels of automation. The results show that risk compensatory adaptation is significant if the computer of the safety system not only provides warning, but also performs safety control actions when necessary. In addition, even if the automation functions properly, new types of accidents arise, so that the number of accidents may not decline. The second experiment examines the dependence of human adaptation to a safety system on the direction of level shift of automation. The results show that the risk reducing adaptation when the level of automation decreases is not as significant as the risk compensatory adaptation when the level of automation increases