Researchers have solved a puzzle in traffic research, namely why so many people 'jerk' the wheel when they steer a car.
The ability to predict what a driver is going to do in the near future has been in the works since 1947, when British researcher Arnold Tustin (1899-1994) produced the first model for how a person steers towards a target. He identified a continuous and linear control behavior. When a car is driven, this corresponds to the driver gently and continuously following the road with the steering wheel.
This behavior, known as tracking within control theory, has been the prevailing hypothesis for car driving ever since - it just isn't accurate. When comparing the linear model with actual measured data, deviations become apparent, namely jerkiness in the steering signal. Tustin saw these deviations from the continuous prediction as well, but the mystery has remained unsolved.
A new discovery shows that jerkiness while steering is due to an innate behavior humans have when reaching for a target with their hand.
Credit: Henrik Sandsjouml
It's because we are not built to reach for things using continuous and linear control behavior - when we reach for a target with our hands, our jerkiness takes over.
"With the driver model I have developed, it is possible to predict what drivers are going to do with the steering wheel before they do it. It is possible to predict how far the driver is going to turn the wheel, right when the person starts a wheel-turning movement. It's like looking into the future," says Chalmers researcher Ola Benderius. "Imagine a fatigued driver on the verge of running off the road. He or she suddenly wakes up and reflexively initiates a very large corrective maneuver, a potential misjudgment that can lead to something very dangerous. Since we are now able to predict how far the driver is going to turn the wheel, the vehicle's support systems can identify potential misjudgments and intervene, which means a serious accident, such as the car traveling into approaching traffic, can be avoided."
When studying how we humans move our hand from Point A to pick up something from Point B, the speed of the movement has a direct relationship with the distance - the longer the distance, the quicker the movement. The interesting effect of this is that the time for the movement is the same regardless of the distance.
"We immediately recognized this pattern from our measured steer signals," says Ola Benderius. "It was a bit of a eureka moment. Was it possible that this basic human behavior also controlled how we steer a car?"
With the idea in mind, Ola Benderius extracted over 1,000 hours of car and truck driving from real driving data, which resulted in 1.3 million steer corrections. It turned out that 95 per cent of these correspond with the 'reaching' theory. Ola Benderius and Gustav Markkula had discovered that steering is not linear when the driver follows the road, but rather that the driver turns the wheel according to the special reaching pattern.
"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," says Ola Benderius. "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."
With this new knowledge, he was able to develop a mathematical model that can explain many observed steering behaviors, which means that the driver response to different situations can be predicted before it occurs. Ola Benderius believes the discovery will have an impact on an entire research field.
"This might completely change how we regard human control of vehicles, crafts and vessels. I hope and believe that many researchers will utilize the findings and start to think in new ways. Control behavior has traditionally been studied on the basis of control theory and technical systems. If it is instead studied on the basis of neuroscience with focus on the human, an entire new world opens up. This could push the research field in an entirely different direction," says Ola Benderius.
The research has been conducted within the Adaptive systems research group at the Department of Applied Mechanics at Chalmers University of Technology. It has been financed by the Safer Vehicle and Traffic Safety Centre at Chalmers and the FFI research program.
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