Assessing the spatial equity of Seoul’s public transportation using the Gini coefficient based on its accessibility

ABSTRACT

The purpose of this research is to develop a methodology for calculating the index of the spatial equity for the public transportation services for the city of Seoul using the Lorenz curve and Gini coefficient based on accessibility to the services. The index was estimated for 100 m × 100 m cells first and then aggregated for 424 traffic analysis zones (TAZs) in the city. The indices for Seoul’s subway and bus were represented with and without the weighting factor. On the basis of this methodology, this study assessed the effect of an additional subway line on the spatial equity before and after its operation. Furthermore, an index of relative difference indicating the change in population and employment in the station areas was applied to investigate the changed effects of spatial equity between population and employment from the new subway line. The core findings from this research are summarized as follows. First, the subway network of Seoul provides more unequal public transportation services for the TAZs than for the bus network. Second, an improvement in the operation frequency of both transit modes would deepen the spatial inequity of Seoul. Third, a subway extension plan for Seoul could noticeably reduce the spatial inequity. The plan would improve the spatial equity for the population more than that for employment. The most important meaning of this study is to be found in combining spatial equity on the supply side with transit-oriented development (TOD) on the demand side. So, by establishing a TOD policy for the additional subway station areas, an appropriate land-use pattern can be established for maximizing potential ridership in consideration of the combination.

KEYWORDS:

• Spatial equity
• TOD
• transit
• accessibility
• the Lorenz curve
• Gini coefficient

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1 This ArcToolbox tool in ArcGIS 10.1 (ESRI) calculates a magnitude per unit area from point features that fall within a neighborhood around each cell. The parameters for the point density analysis are as follows (Input point features: the subway stations; Population field: the amount of passing traffic per hour at each station; Output cell size: 100 m; Neighborhood: Circle; Radius: 1000 m; Area units: SQUARE_MAP_UNITS). In addition, the Zonal tool in ArcGIS is used to convert the result of point (or line) density analysis at the cell level to spatial subway accessibility at the TAZ level. The parameters are set as follows (input feature zone data: the polygon data at the TAZ level; Zone field: the ID of each TAZ zone; input value raster: the result of point (or line) density analysis; Statistics type: MEAN).

2 This ArcToolbox tool in ArcGIS 10.1 calculates a magnitude per unit area from polyline features that fall within a radius around each cell. The parameters for the line density analysis are as follows (Input polyline features: Seoul’s bus routes; population field: the number of passing buses per a hour; output cell size: 100 m; Radius: 500 m; Area units: SQUARE_MAP_UNITS).

Additional information

Funding

This research was supported by a grant (11 High-tech Urban G06) from High-tech Urban Development Program funded by the Ministry of Land, Transport and Maritime Affairs of the Korean government and the Mid-career Researcher Program (NRF-2015R1A2A2A04005886) funded by Ministry of Science, ICT and Future Planning.