We found that the steering vibration was effective for warning of lane-departure situations, especially when drivers did not know the meaning of warnings. It seems that many drivers have their own Mental Model for response to a haptic stimulus transmitted through the steering wheel. This mental model causes drivers to think that the vehicle is deviating from the lane when steering vibration was used as the warning signal. We can conclude that the mental model for the warnings should make interpreting vehicle conditions easy, especially when the haptic warning is transmitted through the steering wheel. © 2003 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved.