**5. Conclusions**

The governmen<sup>t</sup> of Seoul has been operating the AFC system and open data platform since 2004 and 2013, respectively. These systems provide the opportunity to analyze the e fficiency of station areas in terms of TOD. This research was conducted to evaluate the transit e fficiency of subway station areas. A total of 352 subway stations within a 500-m radius in Seoul were analyzed. Socioeconomic data were obtained from the open data platform, i.e., population density, land value, number of households, and number of companies. Transit-related data were obtained from Seoul's smartcard data, i.e., the number of subway lines, the number of bus lines, and the number of bus stations. Given the TOD concept, the transit e fficiency evaluation was designed as a two-stage network slacks-based measure data envelopment analysis (NSBM DEA). The first stage was designed as a transit-design evaluation and the second stage was evaluated with respect to transit e fficiency.

The results of the evaluation were as follows: the overall e fficiency score and S.D. were estimated to be 0.349 and 0.207, respectively, which points to a large gap between the e fficient and ine fficient station areas in Seoul. The analysis results indicated that the eight e fficient dongs were characterized by both residential and commercial land use. In addition, overall e fficiency was found to be high in areas that have both residential and commercial characteristics. The non-scoring dongs were identified as having top priority for TOD, and the land-use features of these dongs are residential. Dongs with overall e fficiency scores in the 0.0 to 0.2 range were designated as second-priority areas, and these dongs also have commercial features. Based on the results of the transit design and e fficiency evaluation, it was possible to determine the TOD-related priorities for stations and dongs.

Considering the regional characteristics, development e fforts are also required to improve overall efficiency. This research measured transit overall e fficiency based on transit design and e fficiency. From the results, recommendations regarding the TOD priorities and development directions were made by station areas. Although various factors were used to evaluate TOD efficiency, a variety of additional socioeconomic and transit factors must also be considered. In this study, we defined the station area as the area within a 500-m radius adjacent to a subway station based on previous literature. The overlapping areas may affect the results of the analysis. The score of a station area that contains multiple stations would be different from the score of a station area that only contains one station. Based

on the sensitivity analysis, the effect of the station area should be investigated. The weight of each stage of NSBM DEA model can be also changed according to regional conditions, environment, and culture.

**Author Contributions:** For The authors confirm the contribution to the paper as follows: Study conception and design: E.H.L., H.S., S.-H.C., S.-Y.K., D.-K.K.; Data collection: E.H.L., H.S., S.-H.C., D.-K.K.; Analysis and interpretation of results: E.H.L., H.S., S.-Y.K., D.-K.K.; Draft manuscript preparation: E.H.L., H.S., S.-H.C., D.-K.K. All authors reviewed the results and approved the final version of the manuscript.

**Funding:** This research was supported by a gran<sup>t</sup> from R & D Program of the Korea Railroad Research Institute, Korea.

**Conflicts of Interest:** The authors declare no conflict of interest.
