Weighted Two-Dimensional Longitudinal Impedance for Driving Support System * J.C.F. de Winter, M. Mulder, M. Mulder, M.M. van Paassen Aerospace Engineering Control and Simulation Division Delft University of Technology Delft, The Netherlands j.c.f.dewinter@student.tudelft.nl T. Yamamura Chassis Control System Development Group Advanced Vehicle Engineering Department Nissan Motor Co., Ltd. Yokosuka, Japan t-yamamura@mail.nissan.co.jp * 0-7803-8566-7/04/$20.00  2004 IEEE. Abstract - Visual cues that are relevant to safe car driving are generally not supported by redundant non-visual cues, resulting in increased accident risk when visual attention is misallocated. Haptic gas pedal feedback, also referred to as longitudinal impedance, may assist drivers in proper and timely reallocation of their visual attention. A solution is presented for translating the relevant two-dimensional situation in front of the driver into a total hazard level from which gas pedal feedback force is calculated. Car driving simulations, that include a RADAR-like sensor model and a human driver model, were performed for several highway maneuvers. The simulations indicated that the calculated gas pedal feedback force is a weighted mix of hazard-defining variables depending on the positions of the lead vehicles in front of the own vehicle. Keywords: Haptic feedback, car driving, man-machine interfaces, automotive environment. 1 Introduction Nowadays much investigation is done by leading automobile manufacturers into lane following and rear-end collision avoidance systems which – when introduced on a large scale – are expected to reduce accidents by a minimum of 30 percent [7] and reduce the number of fatal accidents in traffic up to 45% [6]. Haptic gas pedal feedback, also referred to as (longitudinal) impedance, as a (non-visual) driver support system, concerns the alteration of external gas pedal feedback force according to the hazard level with respect to the own vehicle. The haptic feedback is supplied through the longitudinal control channel itself, such that the driver gets direct cues of changing hazard while remaining in full control of the vehicle. Haptic feedback may support the driver in reallocating attention and may allow more room for assessing the situation, and choosing the appropriate response. Earlier studies have been performed that deal with calculating a total hazard or avoidance vector of the situation in the two-dimensional (2D) plane by using a potential/hazard field method and superposition principle [3], [5], [8]. Problems arose in defining a consistent hazard level due to the relatively large differences in longitudinal and lateral velocity that belong to car driving. 2 Longitudinal impedance Other solutions that do not feature a 2D potential field for dealing with haptic feedback from the 2D plane have been evaluated. 2.1 One-dimensional impedance A simple solution for dealing with feedback from the 2D plane is taking into account one vehicle only, typically the nearest vehicle, or the vehicle that is contributing most to the total hazard, within a certain area in front of the own vehicle. Such a system, relying on measured variables i.e. time headway (THW) and time to contact (TTC) of one vehicle only for calculating feedback force will be referred to as a one-dimensional (1D) impedance system (Figure 1). A 1D impedance system induces feedback discontinuities when the own vehicle or a lead vehicle moves laterally. A cut-in of a second lead vehicle for example results in a sudden increase of pedal force, because of the sudden increase in the calculated hazard level when the cut-in vehicle becomes the nearest or most hazardous vehicle. Several disadvantages of a sudden large increase or decrease of pedal force might exist, such as misunderstanding of the signal when the driver is paying attention to another vehicle and an increased risk for shock reactions and unwanted reflexes. Furthermore large pedal force gradients might lead to greater wear of the pedal actuator. 1D Impedance calculations pedal force sensor output variables of one vehicle (i.e. THW and TTC) Figure 1. Schematic illustration of 1D impedance