Hands on or off the wheel in assisted driving

On-market vehicles today can be equipped with driver assist features such as adaptive cruise control and automatic steering. These cars can assist the drivers by handling the longitudinal control (accelerating and braking the vehicle) and lateral control (steering the vehicle). However, these vehicles are by no means fully automated and the vehicle may at any time require drivers to manually control the vehicle. An example of such a situation is a so-called “Cut-out scenario”, a known difficult situation for current assistance system to handle. For such cut-out scenario, a car in front of the car with driver assistance features suddenly changes lane to avoid a stopped vehicle ahead, leaving the driving assistance feature only a short time to identify and respond to the situation.

Despite the possibility of taking the hands off the steering wheel when assisted by the vehicle, this is today prohibited by law in Europe (see UNECE r79). Therefore, current on-market systems are required to issue a warning to the drivers that are detected not to have hands on wheel for no longer than 15 s. Having hands on wheel could be assumed to lead to faster response when a sudden event requiring driver action occurs. But, does it? In this paper we investigated the effect of a hands-on-wheel requirement on drivers' conflict response in a longitudinal cut-out scenario. Surprisingly we found that drivers started to steer to pass the stationary object in lane at similar point in time, independent on if they were required to keep their hands on the steering wheel or not. In other words, this paper indicates that there is little evidence on that keeping hands on the steering wheel during assisted driving would promote a faster response in a longitudinal scenario such as the cut-out scenario. However, in assisted driving other types of situations may occur that require driver action. For example, the assistance system may incorrectly steer into an area perceived to be the correct lane but that’s not. So far it is unclear whether a hands-on-wheel requirement would lead to faster response in those type of scenarios.

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