ライフサイクルステージ、自動車利用コーホートと交通 : 都市交通における構造変化の解明

The mobility of urban residents has been expanding over time. Kitamura and susilo (2005) have shown that this expansion stems more from structural change (i.e. change in the relationship between travel behavior and demographic factors), than from change in demographic and socio-economic characteristics (for example, attributes of the individuals and households, such as, more women employed, the household size shrinking, and the resident population aging) of urban residents. Urry (2005) went to conjecture that this structural change is due to increasingly prevailing automobility, i.e., conversion of social and economic system and way of life to adapt to the ownership and use of the automobile. In this study, this conjecture is explored by examining automobility characteristics across lifecycle stages and across automobility cohorts over time. The level of automobility is operationally defined in this study in terms of: automobile ownership, total auto travel time, modal split, and the fraction of trip attraction in traditional central city in the study area. The Kyoto-Osaka-Kobe (Keihanshin) metropolitan area of Japan is the study area of this effort. Intra-household interaction has dominant influences on household members' activity and travel, and also it is closely associated with lifecycle stage. Lifecycle stage factor is introduced into the analytical scope of this study and regarded as a main factor through this research. Nine stages of household lifecycle are formulated according to the classification scheme of the family lifecycle stage. The classification scheme utilizes the criteria, which generally are age and marital status of household head, presence and age of children of head, presence of other relatives and non-relatives. On the other side, changing the built environment affects urban residents' travel behavior to a large extent. This study explores how automobility characteristics and travel activity behavior changed across lifecycle stages within different residential areas over time using statistical analyses. The results confirm that the residence area rather than lifecycle stage is a significant explainer for automobile ownership and automobile use. It further suggests that even within each lifecycle stage, change in the automobile use over time is suppressed in commercial and mixed commercial/residential areas. However, the fraction of automobile trips for suburbs, unurbanized areas, and autonomous areas increased over time in the range of 0 to 4 times depending on the lifecycle stage. Younger childless couple stage and all adults' stage are more auto-oriented in suburbs, unurbanized area, and autonomous areas, and this trend becomes stronger as automobility progresses. No significant differences were observed in the numbers of trips for households of the same lifecycle stage across different residential areas, suggesting that similarly active lifestyles exist. The results suggest that household members' age is also a strong explainer for the fraction of auto trips and total auto travel time, through a four variable ANOVA analysis, including lifecycle stage, residence area, time, and age effect. It has been pointed out that the elderly of these days behave differently than the elderly grew up with the automobile and have been using it ever since their habit forming ages. Thus another important factor introduced into this research is automobility cohort which is defined by grouping individuals who turn 20 years old during the time period indicated. Each time period is chosen with respect to the level of automobility. The following five cohorts are developed for the study area and used in the analysis: pre-war (up to 1945), pre-motorization (1946-1960), initial growth (1961-1970), mass-ownership (1971-1980), and multi-car ownership (1980-). Using the repeated cross-sectional data of Kyoto-Osaka-Kobe metropolitan area in 1970, 1980, 1990, and 2000, this study has attempted to offer a possible explanation of the increases in automobility characteristics by examining automobility characteristics of automobility cohorts. In addition, time effects and age effects are introduced into the analysis as in standard cohort analysis. It focused on statistical age-period-cohort analysis using the popular multiple classification APC model. The identifiability problem attendant with the use of APC model was discussed with repeated cross-sectional data. An interesting finding is shown that pre-war and pre-motorization cohorts show little, roughly 6%, increase on the fraction of auto trips and nearly unchanged on total auto travel time over 1970 through 2000, although their household automobile ownership has increased more than 2 times. Initial growth, mass-ownership, and multi-car ownership cohorts show a great growth of automobile ownership, the fraction of auto trips, and auto travel time from 1970 to 2000, but a little surprising result is that mass-ownership cohorts, not multi-car ownership cohorts, s ...