Relationship between transit modal split and intra-city trip ratio by car for compact city planning of municipalities in the Seoul Metropolitan Area

Compact-city planning factors are commonly applicable even to metropolitan areas. In most cases, however, planning policies based on theses factors fail to consider that travel patterns are not uniform in each metropolitan area. Furthermore, the travel pattern of inter- and intra-municipality that results from spatial interaction between a central city and its various sub-centres and suburbs in a metropolitan area has not been fully explored. A consideration of the specific urban system could therefore provide an answer to the question of why certain factors have different effects on the transit modal split and car travel distance between municipalities of a metropolitan area. The aim of this study was therefore to find an effective way to establish compact-city planning policies in municipalities of the Seoul Metropolitan Area (SMA). An investigation of the changed travel pattern in each municipality based on the changed relationship between transit modal split (TMS) and intra-city trip ratio by car (ITR) between 2006 and 2010 found that the SMA became more car-dependent: TMS and ITR of the municipalities declined together, and ITR decreased much more in the outskirts. Based on the relationship between the two factors, the effects of changes in land use and transportation were estimated using a combination of cluster and regression analysis. This revealed that, in municipalities of Seoul and its adjacent sub-centres, there is a need to promote transit-oriented development (TOD) by creating high-density areas within close proximity to city railroad stations. In contrast, it is necessary, in municipalities on the outskirts of the SMA, to restrict large-scale developments, such as large retail centres, and instead promote a mixture of self-sufficient land uses. In the intermediate municipalities that lie between these two, TMS and ITR can be increased through TOD near railroad stations, or ITR alone can be increased through a greater mix of land use. These findings could assist in implementing effective compact-city planning policies in each municipality of the SMA, and could also be applied to the other metropolitan areas in Korea or elsewhere in the world.