It is said to have been a riddle that has puzzled traffic researchers for 70 years – why do people sometimes make inexplicably jerky movements when steering a car? Now, researchers at Chalmers University of Technology in Göteborg, Sweden, believe they have found an answer – one rooted in innate human behavior.

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When maneuvering a steering wheel, both children and adults demonstrate a jerkiness that researchers have previously been unable to explain. A new discovery shows that the jerkiness is due to an innate behavior humans have when reaching for a target with their hand.
Image credit: Henrik Sandsjouml

Researchers are interested in better understanding the instinctive movements of drivers in order to build better safety devices. The ultimate goal of this research is the creation of a safety system for a car that is able to predict what the driver will do next and respond accordingly.

The mystery at the heart of the new study dates back to 1947, when British researcher Arnold Tustin developed the first model to describe how an individual steers toward a target when driving.

Tustin observed a behavior now known as “tracking within control theory,” in which the driver gently and continuously follows the road with the steering wheel while driving. But when this model was compared with measured data from drivers, Tustin found deviations from this continuous and linear control behavior – an inexplicable jerkiness.

Chalmers University of Technology researchers Ola Benderius and Gustav Markkula turned their attention to Tustin’s problem when they recognized similarities to driving behavior from research into the behavioral theory of reaching.

In the reaching studies, researchers found that the speed of the movement of a hand moving to pick something up has a direct relationship with distance. The longer the distance, the quicker the movement. The unexpected consequence of this modulation of reaching speed is that the time of the movement is always about the same, regardless of distance.

Ola Benderius says the pair “immediately recognized this pattern from our measured steer signals.”

“It was a bit of a eureka moment,” he says. “Was it possible that this basic human behavior also controlled how we steer a car?”

For their study, the pair analyzed over 1,000 hours of real driving data from car and truck drivers, which contained 1.3 million steer corrections. The researchers noted that 95% of these steer corrections corresponded to the reaching theory they had previously studied.

From this observation, Benderius and Markkula concluded that when a driver is following a road, steering is not linear. Instead, the driver turns the wheel according to the reaching pattern.

Benderius explains:

We were able to use the theory to explain what researchers had been trying to solve for a long time. This was the answer to the previously inexplicable jerkiness in the control signal. Rather than looking upon steering as continuously following the road, steering corrections seem to be applied in a very predetermined manner.

The control behavior has also proven to be very natural; I saw this in an earlier study where I examined driving behavior in 12-year-olds and their parents.”

From this, the researchers developed a mathematical model that they believe not only explains many steering behaviors, but is able to predict them. “It’s like looking into the future,” claims Benderius.

The researchers believe that, from their findings, it is possible to develop smarter anti-skid systems and systems that can intervene when fatigued drivers misjudge maneuvers.

Benderius says that their model “could push the research field in an entirely different direction,” and that although studies of control behavior have traditionally been rooted in control theory, adopting a new, neuroscience-led perspective could revolutionize this area of study.

“This might completely change how we regard human control of vehicles, crafts and vessels,” he adds. “I hope and believe that many researchers will utilize the findings and start to think in new ways.”