'Takeover time' in driverless cars crucial to safety

Simulations run by a team at the University showed a very broad range of 'control transition times' for participants to resume control of their car. The researchers believe their findings will be important for system designers when considering the lead time needed to take control of a vehicle and suggest the focus shouldn't just be on the average time needed for a person to successfully switch, but rather on the range of resumption times.. Results are published in the journal Human Factors.

Engineers Professor Neville Stanton and Alexander Eriksson found that, under non-critical conditions, drivers needed between 1.9 and 25.7 seconds to take control from automation. Such a large range reflects a variety of driver behaviour and environmental conditions.

The authors observed 26 men and women (aged between 20 and 52) engaged in simulated driving at 70 mph, with and without a potentially distracting non-driving secondary task. They recorded response times as the drivers took over or relinquished control of the automated system. A takeover request was issued at random intervals ranging from 30 to 45 seconds during normal motorway-driving conditions. The authors found that drivers engaged in a secondary task, prior to a control transition, took longer to respond -- posing a safety hazard.

Professor Stanton comments: "We hope our findings can guide policymakers in setting guidelines for how much lead time a driver will need when changing in and out of automation. The challenge for designers is accommodating the full range of response times rather than limiting parameters to mean or median transition times."

The researchers warn that if the lead time for normal non-critical control transitions are decided upon based on data obtained in studies utilising critical situations, there is a risk of unwanted consequences.

Alexander Eriksson explains: "Too short a lead time, for example seven seconds prior to taking control, as found in some studies of critical response time, could prevent drivers from responding optimally. This results in a stressed transition process, whereby drivers may accidentally swerve, make sudden lane changes, or brake harshly. Such actions are acceptable in safety-critical scenarios when drivers may have to avoid a crash, but could pose a safety hazard for other road users in non-critical situations."