Advances being made today in electronic technology are evolving the processes that make vehicles more intelligent, in addition to realizing safer and more comfortable driving. Lane departure prevention systems are also becoming practical due to millimeter-wave radar and onboard forward observation cameras. The U.S. Department of Transportation has implemented a National Automotive Sampling System Crashworthiness Data System (NASS/CDS) for North America that found 10,743 accidents in 2016 involved departure from the road. There were 12,043 fatalities in these accidents. Lane departure prevention systems are expected to make a major contribution to reducing accidents of this kind. Advances are also being made in the development of systems that will enable autonomous driving, and the system to ensure safe and comfortable vehicle operation is being developed. These systems embody great potential for reducing the number of accidents caused by road departure. However, the validity of the systems is largely dependent on the level of acceptance by drivers. System validity will be determined by when they provide driving assistance, how much relaxation will be permissible on the driver's side, given that the driver needs to maintain contact with the steering wheel, and the extent of assistance provided by the system. This paper will discuss research on the minimum necessary contact and contact strength with the steering wheel on the part of the driver when the autonomous system is in operation. Using a six-axis driving simulator employing an actual vehicle, the research conducted tests involving 22 test subjects, and studied the relationship between the status of the driver's contact in terms of steering angle speed and steering angular velocity and vehicle behavior when the system failed. The authors analyzed the influence on avoidance behaviors depending on the state in which the steering is held or not grasped when a person performs avoidance behavior. When the steering torque activates, such as in a curve, the reaction will be faster if drivers touch the hand. In the case of a straight road with no steering torque activating, the result of the difference in reaction time depending on whether they are gazing at the front, regardless of grasping or non-grasping, has been clarified from this research.
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