A Countdown to Manual Driving: How Do Drivers Get “Back-in-the-Loop”?

In automated driving, transitions of control from and to the driver are an important safety issue; studies have shown that drivers are slower to respond to hazards immediately after resuming control. This study explores the use of countdowns to mitigate transition problems before drivers are pushed back into control in a simulated driving task. In order to test the effectiveness of the countdowns, immediately after one of the four countdowns, the driver had to react to a stationary vehicle (TTC 5 s) revealed by a lead vehicle changing lanes. Driver responses were logged and analysed. The results indicate that drivers respond more alike if they have the opportunity cognitively to get back into the loop before they need to respond. However, the signal needs to be perceived by the driver, otherwise it can be missed. Drivers thus need support during the switch to manual control, as a focus on other tasks can cause them to miss signals from the vehicle. If such support cannot come from the vehicle, it needs to come from the infrastructure.