Drivers in semi-autonomous vehicles are slower to respond to unexpected situations on the road, according to a recent study. They were also more likely to have a more panicked response to the situation.

The study, led by David Neyens and Sijun Shen of Clemson University, was recently published in the "Journal of Safety Research." Forty-eight participants took part in a driving simulation to gauge their responses.

As automakers and technology companies work to develop vehicle automation, it is expected that semi-autonomous vehicles will be introduced first. At the higher levels of semi-autonomy, a driver would be able to cede full control to the vehicle but would still have to take over in some situations. Previous studies have shown that drivers would likely catch up on work, read, or otherwise engage in non-driving activities while the vehicle was in autonomous mode, potentially delaying their ability to resume manual control.

The Clemson University study intended to determine how drivers interact with systems in semi-autonomous vehicles and whether these would affect their response to a safety critical event. It also looked at how drivers would be able to respond if they were engaged in non-driving tasks when an emergency situation arose.

Half of the participants in the study had full control of the vehicle during the simulation. The other half were in a simulated semi-autonomous vehicle with adaptive cruise control and a lane keeping assistant. These respondents were asked to watch a video while the vehicle's autonomous systems were engaged.

During the drive, each participant encountered a simulated emergency in the form of a strong gust of wind that pushed the car out of its lane. Drivers in the semi-autonomous vehicles were not only slower to respond to the situation, but also turned the steering wheel more severely to bring the vehicle back into the correct lane.

"Autonomous vehicles are a disruptive innovation – they will fundamentally change a lot about the transportation domain," said Neyens. "Ultimately, we want to improve people's safety. There's a great opportunity in the semi-automated driving system because there are such huge safety implications: it's life or death, not just for the driver or passenger but for anyone in the environment."

The researchers say the findings suggest that secondary behaviors may not be tolerable even in vehicles with a high degree of autonomy, and that it may not be appropriate to allow them until fully self-driving vehicles are developed. The study suggests that vehicle designs, such as warnings or alarms that would appear if a driver takes their eyes off the road for too long, could be used to combat driver inattention.

"For fully automated vehicles, should there be driver education at all? I think so," said Neyens. "But what that will look like in the future is still an important question."