Transit-oriented development (TOD) was initiated to comprehensively address various urban problems, including traffic congestion, dependence on fossil fuels, and air pollution, through a close link with the traffic and urban development in cities that heavily rely on vehicles. TOD was driven by the spread of low-density cities such as in the U.S. Asian countries have become very interested in this urban development planning technique because the urban problems that have recently emerged in their metropolitan areas are similar to those experienced by low-density cities in Western countries. Moreover, the gravity of the problems is rapidly increasing.
The social and economic conditions, urban development patterns, traffic systems, and trip patterns in Asia are different, however, from those in Western metropolitan cities such as in the U.S. While the urban diffusion and traffic system developments in Western metropolitan areas gradually changed after the Industrial Revolution, metropolitan areas in Asia’s emerging countries have rapidly experienced what the Western countries had faced, within a short span of time since the 1960s. In addition, while metropolitan areas in North America have urban problems related to their heavy dependence on vehicles due to the wide scope of their low-density roadway systems, metropolitan areas in Asia have mid- and high-density urban structures, relatively low dependence on vehicles, and various types of mixed traffic modes. Moreover, the metropolitan spatial structure in most Asian emerging countries is monocentric, whereas it is more dispersed or polycentric in Western countries. In other words, the serious traffic problems in Asian metropolitan areas arose from their monocentric spatial structure and insufficient traffic infrastructure. Although their dependence on vehicles is relatively low, their traffic congestion and resulting air pollution are reaching a serious level.
This study was spawned by the following question: Is TOD, which was developed to address urban problems in Western countries, applicable to Asian metropolitan areas? To answer this question, the impact and level of convenience of changes in TOD trip modes in major metropolitan areas in developed Asian countries were determined, after which it was assessed if the alternative approaches could solve urban problems related to the traffic, environment, and energy in the Asian metropolitan areas. The Seoul metropolitan area in Korea, the Bangkok metropolitan area in Thailand, and the Manila metropolitan area in the Philippines were chosen as the target subjects. In particular, the study aimed to prove that TOD can be a tool for a comprehensive approach to solving not only traffic problems but also environment and energy issues.
To compare the changes in the TOD trip behavior in the Asian metropolitan areas and their comprehensive TOD benefits, their traffic development features and the concepts of their TOD strategies and their ongoing policy directions both at home and abroad were analyzed. Based on the analysis results, the TOD planning elements and their indexes were induced, and then the impact of such indexes on the TOD trip behavior was evaluated. For the evaluation, the change module of individual trip behavior influenced by the physical environment and the accessibility of a neighborhood unit of the city was analyzed. The result was used to induce a comprehensive TOD benefit by using the conventional 4-step Traffic Demand Model. The analysis indexes of the trip behavior were categorized by trip generation frequency and choice of trip mode, and their experimental analyses were limited to the Seoul metropolitan area. This is because the data for the two other regions had limited availability. The databases for Manila and Bangkok are still being established, as was the database for Seoul, but the analysis technique for Seoul is not applicable to Manila and Bangkok, since some of the data on individual trip behavior and spatial features in the two cities are obsolete or unavailable. Despite these obstacles, comparison of all the available data that were collected for each metropolitan area was still attempted, with the analyzed results of the Seoul case. In detail, the impact of the TOD physical environment and accessibility on the traffic mode distribution ratio in Bangkok was analyzed using the collected data. For Manila, the comprehensive TOD benefit, driven by the increasing number of railroad users near railroad stations, was estimated using the ASIF model. With the comparison of these analyses with that of Seoul, the changes in the trip behavior and the comprehensive TOD benefits in these two cities were also reviewed.
The analysis of the changes in the TOD trip behavior in the Seoul metropolitan area and the impact of the comprehensive TOD benefit by scenario showed that the TOD plan and policies can also be applied to the two other Asian cities, despite their different environmental conditions. The indexes of the trip behavior are related to each other, however, in a somewhat complicated manner. For the probability model of internal/external trip generation, categorized by trip distance and trip frequency, the external trip ratio tends to decrease due to TOD planning. For the choice of trip modes, however, there are planning elements that increase vehicle trips and show adverse relations. For instance, the probability ratio of internal trips decreases as the population density increases, but reliance on vehicles in external trips increases. In this sense, it is necessary to consider these complicated relations as TOD planning elements are applied to a policy.
To project the comprehensive benefit of TOD, this study also tried to analyze the differences between the traffic, energy, and environmental benefits based on the spatial location scenarios of 120,000 housing projects in the Seoul metropolitan area. The scenarios were categorized into that with increasing population density, that with a modified residential/non-residential mixed ratio, and that with an increasing density of 4-leg intersections, which is an index of a narrow street network. Combinations of these scenarios were also analyzed. The results showed that among various planning elements, the urban development density has a higher benefit than the mixed-land-use index. For example, as the population density increases, the comprehensive benefit reaches KRW26.2-39.1 billion/year. On the other hand, as the residential/non-residential mixed ratio changes, the benefit reaches KRW6.9-9.1 billion/year. These prove that the population density has a more significant impact than the mixed-land-use rate, because the population density has a marked impact on the model shift from vehicles, although it increases the external trip generation rate. In addition, the comprehensive benefit of the scenario, where all the three factors increase, is KRW38.6-61.2 billion/year, which is equivalent to a 147-157% increase. This result indicates that the combination of TOD planning elements can bring about much more benefits. Therefore, it is very essential to apply all the TOD planning elements to the policy in Seoul.
The analysis for Bangkok induced the trip patterns (the impact on the trip model shift ratio) according to the TOD planning elements, based on the available database. This analysis proves the effectiveness of TOD in policies, and also differs somewhat from the analysis of the Seoul case since it shows that the density and accessibility are very important planning elements, among others. For example, unlike in Seoul, the population density, employment accessibility, and in-town trip length to the CBD are the only factors that increase the model shift ratio of public transportation. The elements that influence most the model shift ratio of vehicles are the population density, employment accessibility, and trip length to employment centers. In particular, as the population density and employment accessibility increase, the model shift ratio of vehicles decreases. This implies that the TOD planning elements have a positive impact on trip behavior. Selective application of the TOD planning elements should be considered to improve policy effectiveness, however, rather than applying all the elements in the case of Seoul, since the other TOD planning elements in Bangkok were not considered in the analysis.
The analysis for Manila was carried out to identify how the comprehensive TOD benefit changes in accordance with the increasing number of users of public transportation as development projects proceed around railroad stations. In fact, it was not that easy to secure data on individual trip behavior in the Manila metropolitan area. The comprehensive benefit was KRW65.46 billion/year when the influence area was set at 1 km. The figure increased to KRW90.74 billion/year when the influence area was expanded to 2 km. This was not the experimental analysis using the actual TOD trip behavior or patterns, but was done based on the fact that the changes increased by 5% the public transportation usage index within the station influence areas. Therefore, it is difficult to say that some TOD planning elements are better than others in terms of the comprehensive TOD benefit. This analysis has some implications in terms of showing how comprehensively the increasing accessibility of public transportation influences traffic, energy, and environmental benefits.
From the results of the study on the impact of TOD plans on trip behavior and projections of comprehensive traffic, energy, and environmental benefits, three policies are proposed. First, TOD, which was very seriously pursued in Western countries, can also be applied in Asian metropolitan areas. TOD is a strategic concept that controls a low-density and mono-purpose development, focusing on vehicles, and addresses issues related to the environment, traffic, and energy through high-density mixed land use, focusing on public transportation. As in Western countries, TOD can be applied effectively in Asian metropolitan areas that have a relatively lower model shift rate of public transportation and high-density mixed land use. In this sense, this study is very meaningful because it shows that the TOD development strategy is universally applicable.
Second, this study proved that the development density, among other TOD planning elements, can augment traffic, energy, and environmental benefits by inducing changes in trip behavior. The analysis for Seoul showed that the increase in the population density more significantly increased the benefit through the trip model shift. The analysis for the Bangkok metropolitan area showed the same possibility. In short, population density can consistently induce the reduction of vehicle use and increase in public transportation use. Accordingly, efforts must be made to apply TOD planning in Asian metropolitan areas, especially with respect to the development density.
Third, based on the experimental analysis of the TOD planning elements, this study implies the need to formulate diverse policy strategies for Asian metropolitan areas, since these elements have various impacts on the choice of trip mode, the trip degeneration frequency, and the trip distance. For example, if the results of the analysis for Seoul were presumed to be the same as those of other Asian metropolitan areas, the traffic policy for the reduction of dependence on vehicles can be changed in accordance with which trip behavior are preferred to be modified. In other words, when an attempt was made to address traffic congestion by reducing the trip distance, it was necessary to set up a policy that emphasizes the mixed-land-use ratio rather than the population density. On the other hand, when an attempt was made to shift the trip models, a policy focused on the development density was needed. This is because a decrease in the trip distance can promote trip self-sufficiency, and a trip model shift tends to reduce dependence on vehicles. When these two strategies are applied at the same time, however, the impact can be offset due to their complicated effects. Therefore, a more effective and achievable strategic approach is needed to identify the serious traffic issues that metropolitan areas are facing. The comprehensive approach that uses the TOD planning elements tends to increase the overall traffic, energy, and environmental benefits, but the impact should be closely reviewed and applied through a cost-effective approach.
This study was limited in two aspects: data availability and policies for practical application. The initial purpose of this study was to assess the possibility of TOD application and to discern patterns in the three selected cities (Seoul, Bangkok, and Manila) using a single analysis methodology and the same data. There were some limits in securing data for the current year, however, so the final result was induced through a partial comparison. Therefore, another study must be conducted to address the limits of this study. In addition, it was not sufficiently revealed in this study that the metropolitan areas have different TOD planning elements. Of course, the study should be continued to disclose the origins of the analysis results. In this regard, a more in-depth study should be conducted to determine why the statistical similarity, direction, and size of the TOD planning elements can have distinguishable impacts, depending on the history, culture, and social and economic conditions of the city.
This study also proved that TOD plans induce changes in trip behavior that can have traffic, energy, and environmental benefits. To ensure that these plans would be applied, however, the systemic conditions and problems should be analyzed and relevant studies to come up with improvement measures should be conducted. These were not addressed in this study, since its purpose did not include the suggestion of strategies for realizing TOD. The identification of the system conditions and the study of improvement measures are indispensable, though. Therefore, the future study should review the systemic conditions of urban development, the planning of traffic facilities, and financing methods. In addition, of course, efforts to come up with measures for applying TOD are needed.