Hold to continue – safety aspects of cooperative human machine systems in urban traffic

The complexity of urban traffic will present highly automated vehicles with major challenges. Ambiguous situations with unclear behavior from other road users can push the vehicle to its system limits. Temporarily involving the vehicle user in the driving task may help to cooperatively overcome system limits, but must not lead to increased risk. In a driving simulator study, we investigated two cooperation strategies, differing in terms of the user involvement. In the one strategy with low involvement the users were holding a button to continue driving, whereas in the strategy with high involvement, the user temporarily performs the entire driving task with steering wheel and pedals. Participants experienced these cooperation strategies in five ambiguous scenarios and rated them regarding safety aspects and dimensions of user perception. The strategy with high involvement is associated with more critical encounters including crashes. The strategy with low involvement is among others associated with higher ratings in perceived safety, perceived control and comfort, lower ratings on mental demand and is generally preferred by the participants. The study provides insight into safety and control aspects of cooperative systems and raises questions about the extent of user involvement.