Effects of Non-Speech Auditory Cues on Control Transition Behaviors in Semi-Automated Vehicles: Empirical Study, Modeling, and Validation

In semi-automated vehicles, non-speech sounds have been prevalently used as auditory displays for control transitions since these sounds convey urgency well. However, there are no standards of specifications for warning sounds so that diverse non-speech sounds are being employed. To shed light on this, the effects of different non-speech auditory warnings on driver performance were investigated and quantified through the experimental study and human performance modeling approaches. Twenty-four young drivers drove in the driving simulator and experienced both handover and takeover transitions between manual and automated modes while performing a secondary task. The reaction times for handover and takeover, mental workload, and subjective responses were reported. Overall, a traditional warning sound with many repetitions and an indicator sound with decreasing polarity outperformed and were preferred. Additionally, a mathematical model, using the Queuing Network-Model Human Processor (QN-MHP) framework, was applied to quantify the effects of auditory warnings’ acoustic characteristics on drivers’ reaction times in response to takeover request displays. The acoustic characteristics, including the fundamental frequency, the number of repetitions, and the range of dominant frequencies were utilized in modeling. The model was able to explain 99.7% of the experimental data with a root mean square error (RMSE) of 0.148. The present study can contribute to establishing standards and design guidelines for takeover request displays in semi-automated vehicles