This paper reports result of experiments with a driving simulator in order to answer the following question: What type of support should be given to an automobile driver when it is determined, via some method to monitor the driver's behavior and the traffic condition, that the driver's intent may not be appropriate to a traffic condition? This paper compares soft protection and hard protection from viewpoints to reduce automation surprises as well as to cope with a driver's misinterpretation of warning messages or machine's protective action for avoiding a collision into some other vehicle.