Driver perception of brake notifications under real driving conditions.

The amount of information to be processed by drivers increases with the number of driver assistance systems (DAS). This implies that all relevant perception channels have to be used to convey information. The paper's contribution is to enable system designers to use differences in longitudinal acceleration as an information element in DAS. We conduct a study of the actual application context and examine the perceptible difference in longitudinal acceleration (kinaesthetic distortion). Thereby, we discuss dependencies of the perceptible difference on speed and acceleration immediately before the distortion. Furthermore, we investigate the spread of perceptional performance of different drivers. The results demonstrate smaller perceptible differences in acceleration at higher speed and weaker perception when the acceleration immediately before the warning is greater. This paper aims to provide a guideline for the implementation of brake warnings for informative DAS and for the adaption of the brake intensity according to current vehicle dynamics. PRACTITIONER SUMMARY: This paper aims to enable the kinaesthetic perception channel for informative driver assistance systems. A real world driving study reveals the perceptible difference in longitudinal acceleration (kinaesthetic distortion) depending on vehicle speed and acceleration and serves as a guideline for applying brake warnings as an information element in vehicles.

Intuitive steering assistance in critical understeer situations.

OBJECTIVE: To develop and verify a driver assistance function, working on the electric power steering of passenger cars, to support the driver on handling critical understeer situations. The main objectives of the so-called understeer assistance are reinforcing the driver's awareness of the driving conditions and giving support to handle the situation correctly without inducing irritation by abnormal steering behavior. METHODS: The system was designed in consideration of psychological aspects of human decision making while operating a vehicle in unfamiliar understeer situations. Using a comparison of vehicle dynamics with a reference model computed in the car, the level of understeer is calculated. Depending on the understeer level, the steering wheel restoring torque is increased while a vibration is applied to the steering wheel at the same time. To verify the achievement of the objectives, the standard steering system is compared to the developed understeer assistance in an active driving study on a test track. Not only objective measurement data but also subjective ratings delivered by 63 unbiased participants were used. RESULTS: The subjects follow the offered steering recommendation by steering less when the assistance function is activated (Δγmax = 44.38°, p = 2.5°·10⁻³%). In the sequel, an enhanced vehicle reaction arises that is validated by analyzing the achieved maximum lateral offset (ΔSy,res = 0.16m, p = 0.07%). In addition, the evaluation of subjective ratings clearly indicates a better awareness of the understeer situation with the assistance function (χ= +0.44, p = 0.89%). Furthermore the subjects rate the understeer assistance better than the standard steering system (χ= +0.43, p = 3.03%). CONCLUSIONS: By measuring vehicle data and eliciting subjective opinions of the participants, the effectiveness regarding an improved handling of an understeering vehicle as well as the acceptance of the understeer assistance by the driver is confirmed. Larger subject groups and more realistic boundary conditions should be considered for additional evaluations. The approach of using standard vehicle hardware to adapt the vehicle to specific driving situations under consideration of psychological aspects of human decision making should be investigated further.