# Analysis of the Motion Sickness and the Lack of Comfort in Car Passengers
## 1 Introduction  
Research on new generation of vehicles has been mainly focused on vehicle collision avoidance, lane keeping, coordination control or energy-efficiency with less attention paid to comfort [1, 2, 3]. Therefore, although the comfort-based strategies have not been the predominant control policies, they have to be considered in future vehicles, since when other activities are being carried out or no attention is paid to the trajectory both lack of comfort and motion sickness play a bigger role. Proof of this is the actual effort of vehicle manufactures to improve the vehicle comfort [4, 5]. Quantifying the lack of comfort is a very challenging topic because it depends on the human perception and is affected by several factors. In [6], some types of human-vehicle interaction variables that influence the user's comfort are analyzed: human factors (as age and gender), environmental factors (as temperature, noise and pressure), spatial factors (as work-space, seat shape, etc.) and dynamic motion factors (usually named ride comfort). In [7], [PERSON] et al. define ride comfort as the overall comfort and well-being of the vehicle's occupants during vehicle travel, whereas in [8], [PERSON] defines it as that part of the comfort construct that can be related to technically measurable or experienced vehicle movements, such as queasy static accelerations, shakiness and vibrations, as well as jerks. In [9], two terms have been used: discomfort (also named average discomfort), which isdefined as a general feeling of not well-being, and motion sickness, that is associated with dizziness, fatigue and nausea. The lack of comfort is associated with the frequency of the vibration and is directly proportional to the intensity of it. Furthermore, it has also been observed that increasing the time of exposure to vibration results in an increase of discomfort. It is known that low-frequency vibrations close to 1 Hz are transmitted throughout the body increasing malaise, while higher frequency vibrations are attenuated by the human body. It is also interesting to note that monotone continuous low-frequency vibrations increase fatigue, while transient vibrations produce stress [10]. Moreover, the human body responds differently to vibration frequencies depending on which body part and in which direction the force acts. How the frequencies affect humans depends on the proportions of a person's body and the type of frequency that affects the person [11]. While the fully automated vehicle (AV) is the future of the automotive industry, there is uncertainty regarding how the vehicle will be operating [12]. There is a strong correlation between the comfort and acceptance of autonomous vehicles [13; 14]; so, if the factor affecting passengers' discomfort is known and the driving control strategy is accordingly improved, the riding comfort of passengers will be improved [15]. Research on the ride comfort of vehicles based on traditional drivers can provide a powerful reference for improving the algorithm design of the ride comfort of autonomous vehicles [15]. In [5], factors that could influence the comfort of autonomous vehicle motion are mentioned: acceleration, speed, quickness, vertical loadings, type of maneuver or driving style between others. It is also mentioned that given that these findings are based upon a limited number of research studies of various levels of realness, further evidence is required to confirm these factors. Ride comfort analysis has been performed from different perspectives, being vehicle dynamics and the interior environment of the vehicle the most significant research lines. Thus, both the vehicle dynamics and the characteristics of the seat are also widely analyzed in several works, due to their influence in vibrations transmission [16]. Vehicle suspension designs have been proposed in [17] and experiments on seat structure suggest its influence on ride comfort measurements [18].