Development of a Structural Equation Model for ride comfort of the Korean high-speed railway
Introduction
The concept of ride comfort varies depending on time, country, culture and physical condition of passengers. The patterns of train rides have gradually diversified and studies on ride comfort have been progressing in various aspects. However, studies on ride comfort for high-speed trains are relatively rare due to the fact that only four countries, before South Korea, were operating high-speed railways (France: TGV; Spain: AVE; Japan: Sinkansen; and Germany: ICE) with few customer complaints regarding ride quality. The KTX, which operated in South Korea, is the first high-speed train based on the French platform, the TGV. There were some issues raised from passengers who were not familiar with the European style of the cabin interior and the seat design. After a year of the KTX operation, many issues have been raised, all of which can be largely divided into two categories; (1) problems with the rolling stock seat, and (2) problems with the cabin interior (KRRI, 2004). For the rolling stock seat, the major issue was the reduction of an on-time operation ratio due to the frequent occurrence of problems. As for the cabin interior, several issues have been brought up: (1) the negative effect of ride comfort due to the noise generated by many tunnels (specific geological characteristics of the Korean peninsula), (2) the occurrences of motion sickness related to backward seats, (3) the inconveniences related to seats that did not consider the anthropometry of the Korean population, and (4) the inconstant speed (Korail, 2004).
Many studies on ride comfort and seat convenience produced in the past contributed to the improvement of seat design and convenience (Corlett and Bishop, 1976). Branton's (1969) study on ride comfort suggested that ride comfort was related to the deficiency of passengers' experiences or the low quality of seats. Thus, the ride comfort of the seats was evaluated with various methods. These evaluations focused on assessing the degrees of discomfort. Several other studies tried to evaluate positive seat comfort (Zhao and Tang, 1994). Zhang et al. (1996) studied a model for the perception of comfort and discomfort based on the results of Zhao and Tang's study, as well as their own assumption that discomfort was related to the lack of satisfaction from biomechanical factors such as joint angles, muscle contractions and pressure distribution that generates pain, soreness, numbness, and fatigue. On the other hand, comfort was also surveyed to be related to feelings such as relaxation and physical well-being (Metzger, 1994). Peter (2004) conducted a study focused on testing the posture of passengers for cabin design. He evaluated the degree of satisfaction for seat posture with qualitative questionnaires. The results were then implemented in seat designs. Cowings et al. (2001) evaluated the degree to which carsickness affected the performance and emotional state of soldiers during C2V (Command and Control Vehicle) operation. Symptoms that were revealed as hindering factors to ride comfort were drowsiness, headache, nausea, upset stomach, and the effect of the surrounding temperature. In a psychological study related to ride comfort, Looze et al. (2003) analyzed that perceptions of comfort and inconvenience were acquired from the following (including existing information): visual, auditory and olfactory stimuli, current mental status, temperature, moisture, pressure, posture, and movement.
Most of the previous studies demonstrated that ride comfort is a complex emotional state involving various factors such as personal characteristics, hardware design factors, driving environment, etc. It is also important to note that the term ‘ride comfort’ was used synonymously with ‘ride satisfaction,’ ‘seat comfort,’ ‘comfort,’ ‘passenger comfort,’ and ‘ride quality’ (CEN, 1996a, CEN, 1996b, CEN, 1999, ISO 2631-1, 1997, Johan, 2000). In order to minimize confusion with terminology, ride comfort in this study is operationally defined as the state of ‘a pain-free seat environment that is free from physical and visual fatigue to provide a substantial degree of comfort’ (Yun et al., 2004).
There have been a number of studies regarding comfort, ride comfort, ride quality and ride satisfaction for vehicles and transportation systems. However, very few studies have been conducted on the aspects of specific methodologies to quantitatively evaluate ride comfort. Also, previous studies have had some limitations on analyzing ride comfort, a complex concept that includes passengers' subjective sensibilities (passenger fatigue, body status, ride satisfaction, etc.) as well as regional characteristics of the place where the train is running.
Based on this background, it is necessary to develop a quantitative evaluation method that investigates the causality of diverse factors (form of seats, design of compartment, tunnel effect, etc.) related to high-speed train rides. This study proposed an approach to modeling the complex concept of ride comfort. For data collection, this study used an on-board questionnaire on ride comfort (excluding the technical problems of the rolling stock seat). The pilot study examined factors related to ride comfort and the main survey examined the degree of relationship among the factors based on Structural Equation Model (SEM). Finally, this study proposed a model that consists of the examined factors (form of seats, design of compartment, tunnel effect, etc.).
Section snippets
Experiment design
One hundred and seventy-nine and 453 passengers participated in the pilot survey and the main survey, respectively. Table 1 shows the pilot survey and main survey data.
The ambient factors and seat factors were identified by point of view of the cabin design engineers (Korail Co.) and by the results obtained from related studies (Zhang et al., 1996, Johan, 2000, Cowings et al., 2001, Looze et al., 2003, Peter, 2004). Two characteristic variables were added: (1) the tunneling effect that often
Statistical analysis
Based on the results of the survey, the hypothesis was tested by verifying the causalities among each latent variable and executing confirmatory factor analysis. Some cases were determined to be outliers (30 out of 453 cases) and were removed from the group of measurement variables, and the values of measurement variables with different scales were normalized. The outliers were eliminated by the analysis of the univariate outlier and multivariate outlier (Kline, 2005). The outliers were removed
Discussion and conclusion
A SEM technique was used to distinguish variables that affect the ride comfort of high-speed trains directly or indirectly. The results of the analysis, which indicated the suitability of the ride comfort model for each path based on several factors, were significant in the confidence range of 90%. The results of the study also indicated that, in terms of subjective responses, seat pitch, seat width and seat shape (reclining seat) affected the improvement of ride comfort most significantly. The
Acknowledgments
The authors would like to acknowledge the kind support of the KOrea RAILroad (KORAIL) National-2004-425 (the ergonomics study of the ride comfort model development for Korea high-speed rail). This study was jointly funded by KORAIL, KOSEF (KOrea Science and Engineering Foundation), and the Seoul R&BD Program (u-Computing Innovation Center).
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