# Analysis of the Motion Sickness and the Lack of Comfort in Car Passengers
## 2 Comfort Evaluation Methods  
The comfort is usually evaluated, qualitatively, by using subjective rating tests [36] or, quantitatively, by using electrical accelerometers combined with the international standards [37; 38]. The standards describe passenger comfort objectively, but cannot characterize human sensitivity differences for the same vibration, which often depend, for example, on the age, the gender and the weight of the passengers. Two main standards are used in order to evaluate human exposure to whole-body vibration: the British Standard 6841 (BS 6841) [38] and the International Standard 2631 (ISO 2631) [37]. Both define methods for the measurement of vibrations and explain how to process measured data, to standardize quantified performance measures concerning health, perception, comfort and motion sickness. In this work, the ISO 2631 is used. The quantified performance measures of ISO 2631 are based on frequency-weighted root mean square (RMS) computations of acceleration data as Equation (1) shows  
\[a_{w_{i}}=\left(\frac{1}{T}\int_{0}^{T}(a_{i}(t),w_{i})^{2}\ dt\right)^{1/2} \tag{1}\]  
where \((a_{i}(t),w_{i})\) is the acceleration in the \(i\)-th axis weighted with \(w_{i}\) filter in m/s\({}^{2}\) and \(T\) denotes the time range of the measurement in seconds. In this work, both motion sickness and general comfort are studied. Figure 1 summarizes the proposed ISO filters: \(w_{d}\), the filter which evaluates the lack of general comfort for a seated passenger when accelerations are applied in longitudinal or lateral directions; \(w_{k}\), the filter to assess the accelerations in vertical direction and \(w_{f}\), the filter used in vertical direction but for motion sickness evaluation. As for general comfort, the \(A_{v}\) parameter is presented. It accounts for the total weighted acceleration considering three orthogonal axes: vertical, lateral and horizontal axes. As it is expressed in Equation (2), the measured accelerations are first weighted with the corresponding filters and then multiplied by some factors which have to be taken into account as the perception of the acceleration depends not only on the place where the accelerometer is located but also on the direction of the measurement. \[a_{v}=\left(k_{x}^{2}a_{w_{x}}^{2}+k_{y}^{2}a_{w_{y}}^{2}+k_{z}^{2}a_{w_{z}}^ {2}\right)^{1/2} \tag{2}\]  
where \(a_{w_{i}}\) is the weighted acceleration in the \(i\)-th axis in m/s\({}^{2}\) and \(k_{i}\) are multiplying factors. Depending on its value, according to the ISO 2631 Standard, the ride comfort can be classified with different comfort grades as Table 1 indicates [42]. This standard can be used individually or in combination with acceleration and jerk peaks. In [43], a fore-and-aft and lateral ride comfort is evaluated using a methodology \begin{table}
\begin{tabular}{l l} \hline \hline
**Range (m/s\({}^{2}\))** & **Description** \\ \hline greater than 2.0 & extremely uncomfortable \\
1.25–2.5 & very uncomfortable \\
0.8–1.6 & uncomfortable \\
0.5–1.0 & fairly uncomfortable \\
0.315–0.63 & a little uncomfortable \\ less than 0.315 & not uncomfortable \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comfort index (\(A_{v}\)) and its relation with general discomfort [42]. Figure 1: Filters proposed by ISO 2631 [37] and [PERSON] in [35; 39; 40; 41]. based on acceleration thresholds. A too high value of acceleration or jerk can cause discomfort because the passenger will find it difficult to maintain posture. Limit values vary among studies. In [44], a maximum acceleration value of 1.47 m/s\({}^{2}\) is defined, whereas in [9], the threshold is set at 2 m/s\({}^{2}\), as it is argued that, since passengers are seated when traveling in an automobile, the limit should be higher than the limit for trains and buses. Motion Sickness Dose Value (\(MSDV\)) is a measure of the likelihood of nausea.