Causal Mechanism of Motorization in the Medium-sized Local Cities of Japan

Abstract

Since the high economic growth period in Japan private motorcars have proliferated in the local cities, where they have become necessities of life for most dwellers today. This paper considers the present state of proliferation by applying some statistical methods to a set of cross-sectional data, an array of transportation and socio-economic variables in 1990 for each of eighty-four medium-sized cities located outside major metropolitan areas (Table 1). In order to solve the problem, the author studies the systematic relationship among the variables or the transportation system. The results may be summarized as follows:First, the eighteen variables on attributes of household, proliferation rate of private vehicle, modal choice in commuting, urban form, road environment and public transit shown in Table 2 were defined as indicators of the transportation system. Using exploratory factor analysis, they were grouped and simplified into five common factors which can be used as sorts of latent variables. The results of the factor analysis are given in Table 3. Of five factors extracted, Factor 5 was not identified even after a promax oblique rotation. Factor 1 was identified as household car ownership, Factor 2 as private traffic generation and traffic restraint, Factor 3 as public traffic generation, Factor 4 as compact car (Kei-jidosha) ownership in suburbs. These four factors correspond to essential elements of the above-mentioned transportation system.Second, for the respective group of key variables comprising each factor, the causal sequence in their internal correlations was examined by means of path analysis to clarify a property of the element. The following became clear after the investigation of the four arrow diagrams in Figure 1 to Figure 4 that show the results of the analysis: (1) The level of household car ownership is influenced by the number of commuters in the household and the family income. In particular the income level has an effect on the proliferation rate of passenger cars. (2) The incidence of traffic accidents is influenced by the model choice of motorcycles in commuting and the level of traffic congestion. This causal relationship is consistent with empirical facts. (3) The level of proliferation of both bus and taxis is influenced by the D.I.D.'s population density. It was proved that the urban form affects the level of public transit service. (4) The level of household compact car ownership is influenced by the proportion of the D.I.D.'s area to the city area. That is, the larger the proportion is, the higher becomes the level.Third, the relationship among elements of the transportation system was illustrated by hypothesizing a causal model for latent variables derived from the factors and then testing it through the multiple indicator method. The results in Table 4 and Figure 5 were obtained empirically, and indicate that three latent variables derived from the first three factors have significant relationships causally. The model represents a link in the chain of the causal cycle in which proliferation of private motorcars causes loss of public transit passengers.Finally, the first latent variable scores for the eighty-four cities were estimated and examined. This latent variable, household car ownership, is a key exogenous one which precedes causally. Figure 6 shows the highest scores to be located in the northern Kanto, the Hokuriku, and the Tokai Districts, the lower ones generally in Northeastern and Western Japan. Furthermore, cities with higher scores are those in which the secondary activities in the economy are of great importance and the increase in population is remarkable (Table 5).