Visual In-car Warnings: How Fast Do Drivers Respond?

We investigate how quickly drivers can change lanes in response to a visual in-car warning. Our work is motivated by technological developments, in which beacons along the road can trigger in-car warnings, for example when a driver is approaching a lane closure. What is not known, however, is at what distance such an in-car warning still allows for a timely lane change. We measured how quickly drivers respond to a visual in-car warning in a driving simulator. The driving task was combined with an audio task that provided different levels of cognitive distraction. We found that the initial reaction time to in-car warnings was significantly larger for drivers that were distracted by the audio task. Although the majority of drivers responded in time for a safe lane change, some drivers occasionally missed these signals, pointing at a serious potential hazard. Indeed, the results of a simulation model, used to investigate how this might extrapolate to regular traffic conditions, suggest that around 50% of drivers might not make a timely lane change in response to a last-minute warning. This indicates that these signals might be insufficient on their own when applied in the real world. This work can inform the design and evaluation of safer roads and in-car interfaces.