Abstract— To reduce rear-end crash of automobiles, it is important to judge necessity of deceleration assistance as earlier as possible and initiate the assistance naturally. On the other hand, we have derived a mathematical model of driver’s perceptual risk of proximity in car following situation and successfully derived driver deceleration model to describe deceleration patterns and brake initiation timing of expert driver. In this research, an automatic braking system for collision avoidance will be proposed based on the formulated brake profile model and brake initiation model of expert driver to realize smooth, secure brake assistance naturally. It will be shown that the proposed control method can generate smooth profile for various conditions. In addition, experimental results using a driving simulator will show validity of the proposed system based on subjective evaluation. I. INTRODUCTION RIVER assistance systems such as warning system and pre-crash safety system have been developed to reduce and mitigate crashes in road traffic. In the view point of preventive safety, deceleration assistance control is effective when collision risk is high and it is difficult for the driver to avoid it. On the other hand, driver can feel anxiety or nuisance against the system if the initiation timing of automatic brake and/or deceleration profile is not appropriate and it may make the system inefficient. Thus, in order to realize an acceptable and efficient system, it is important to know characteristics of comfortable deceleration behavior and apply them to deceleration assistance system. As a pioneer in deceleration behavior of car driver, Lee [1] developed theoretical framework of drivers longitudinal control based on TTC (Time-To-Collision) associated with visual information. Kondoh et al. investigate the risk perception and showed that it can be represented by TTC and THW(Time-Headway) [2]. Isaji et al.[3] and Wada et al.[4] have proposed a performance index of approach and alienation, KdB as a model of driver’s perceptual risk of a preceding vehicle and its another version, KdB_c based on area change of preceding vehicle on driver’s retina. These indices have been applied to modeling of braking behaviors of expert drivers [5]. Kitajima et al. have surveyed such evaluation indices concerning rear-end collision risk [6]. On the other hand, there are researches concerning design and evaluation of collision avoidance system and Manuscript received March 1, 2009 T. Wada is with Kagawa University, Takamatsu, 761-0396, Japan (phone: +81-87-864-2336; fax: 87-864-2369; e-mail: wada@ eng.kagawa-u.ac.jp). S. Doi, and S. Hiraoka are with Kagawa University, Takamatsu, 761-0396, Japan (e-mail: sdoi@eng.kagawa-u.ac.jp). ACC(Adaptive Cruise Control) system. For example, Goodrich et al. [7] characterized the behavior in a phase plane of TTC vs. THW. Bareket et al. have evaluated efficacy of ACC based on Gipps model that is a car-following model in traffic engineering [8]. Hiraoka et al. derived car-following model for realizing comfortable ACC system by applying concept of minimum jerk model to longitudinal vehicle behavior [9]. Suzuki et al. proposed a method to estimate driver status in car following situation and its application to driver assistance system [10]. It is important to introduce driver’s perceptual risk described before into its design of such driver assistance systems in order to realize comfortable and secure system. To implement this concept, we have proposed a deceleration control method of automobile based on the perceptual risk [11]. In this paper, a brake assistance system will be proposed for preventing rear-end crash based on an expert driver's deceleration model derived from driver’s perceptual risk. Initiation timing of brake assistance will be determined by driver’s brake initiation timing model. Final target status of two vehicles, say, convergence distance by the braking system will be determined based on driver’s risk model. Finally, deceleration profile connecting the brake initiation timing and final target status will be determined by driver’ deceleration pattern model. Validity of the proposed control method will be shown by the experiments using a driving simulator. II. PROBLEM DESCRIPTION Suppose that a driver follows a car in the same lane as shown in Fig.1.Rear-end crash occurs when the driver does not notice the approach of the preceding car due to driver’s errors etc. In such situation, rear-end crashes can be reduced by detecting dangerous situation as earlier as possible and starting to decelerate automatically. To avoid collision, assistance system need to start decelerates earlier than emergency avoidance system such as so-called pre-crash safety system. One of difficulties to realize such system is how to prevent driver’s annoyance. Gap D Vo Vp Fig.1 Car Following Situation A Deceleration Control Method of Automobile for Collision Avoidance based on Driver's Perceptual Risk Takahiro Wada, Shun’ichi Doi, and Shoji Hiraoka D The 2009 IEEE/RSJ International Conference on Intelligent Robots and Systems October 11-15, 2009 St. Louis, USA 978-1-4244-3804-4/09/$25.00 ©2009 IEEE 4881