US Patent 8471909 Driving assistance apparatus

In a hand-free driving warning process for a vehicle, when a grip state of a steering wheel is in a hand-free driving state, and the vehicle is in a travel state stipulated previously, a danger degree is derived based on a position of a vehicle compartment where a non-grip hand exists. In deriving the danger degree, when the non-grip hand is in a high danger position, a high level is set; when the non-grip hand exists in a low danger position, a middle level or a low lever is set. In the low level, any warning is not outputted; in the middle level, a warning is outputted in a sound volume smaller than a usual sound volume; and in the high level, a warning is outputted in the usual sound volume or greater.