Driving is smoother and more stable when using the tangent point

Car drivers can employ a number of strategies to negotiate curves. The tangent point strategy proposes the use of the angle between the tangent point of the inner lane markings and the car's current heading direction, which is proportional to the required steering angle. The gaze-sampling strategy proposes to fixate points on the future path and measure the curvature of optic flow vectors which can inform the drivers whether they over- or under-steer. Nine subjects drove repeatedly on the four loops of a motorway junction for which street parameters were available, while eye-movements, steering parameters and relations of the car to the lane were recorded. In the first half of the trials, we observed which strategy drivers normally use, whereas in the second half, we instructed subjects to use exclusively either the tangent-point or the gaze-sampling strategy and observed their steering behavior. Our results confirm that subjects normally look at the tangent point whereas they do not use gaze sampling of their own accord. Further, subjects drive more smoothly in terms of position on the lane and steering stability in the tangent-point condition.