关键词: 公共空间, 城市基面, 弹性导控, 三维城市设计, 公交导向开发, 公共空间活力, 人性尺度

Abstract: Because guiding and controlling the public spaces in high-density areas focusing on three-dimensional development considers increased density and quality improvement, the new indicators of urban base public space are proposed to supplement the original indicators dominated by the density and floor area ratio (FAR) to guide and control the appropriate development of three-dimensional public spaces in plots adjacent to railway transit.
　　The research summarizes and discusses the calculation methods and corresponding optimization range theory of the public space supply scale in plots adjacent to railway transit formed by the series connection of the three-dimensional walking system and complex and relevant density indicators through a literature review. Based on this action, an indicator set of urban public spaces was created to test the vitality indicator of public spaces.
　　The behavioral data of urban base public space in 33 plots in 11 rail transit stations in Shanghai was collected on site primarily through Gehl-style behavior observation. Next, the public space pyramid of accessibility (Y1), functional visibility (Y2), and continuity (Y3) was developed through dimension reduction. The vitality verification of indicators of the urban base public space helped in a visible scoring to the pyramid model of the case study. Subsequently, the optimization range of the model defined by the peak estimated from curves was observed under different hierarchical tests.
　　According to the test, indicators such as density and coefficients of the plot area and urban base public space are more effective than traditional building density and development intensity, and there is an optimization range. Hence, optimization range indicators were organized to supplement the existing density and FAR indicators to reference practices.
　　In density indicators, the indoor-outdoor ratio of the public space, the indoor density of the urban base public space, and atrium FAR exceed the traditional indicators of building density and development intensity. The correlation coefficient of open public space density is negative. In the range test of curve estimation, multiple indicators have gained the elastic intervals of optimization ranges.
　　These ranges cannot be coordinated and superposed to increase the efficiency for conflicts on accessibility (Y1), functional visibility (Y2), and continuity (Y3). The analysis related to development planning was conducted in this study. The plot area was optimized at 46,000~51,000 m2 (side length: 214~225 m). The outdoor urban base public space area achieved the optimal value at about 30,000 m2. The indoor urban base public space area achieved the optimal value in the range of 0~19,000 m2. However, Y2 shall be improved in the range of 19,000~26,000 m2. The total public surface area achieved the optimal value in the range of 42,500~44,000 m2. The atrium volume reached the optimal range in the bottleneck interval. The atrium FAR reached the optimal value at about 3.85. The indoor-outdoor ratio of the public space achieved the optimal value at about 1.450.
　　The study generally guides and regulates the middle and small-sized plots and high-density development scale and density to appropriate and optimization range, which can bring urban benefit transferring of vitality and flow rate in plots adjacent to railway transit. The developed passenger flows and vitality provide feedback to urban space. Moreover, the large and improved negative development and excessive indoor expansion of siphon activity are avoided.

Key words: public space, urban base space, threshold control, 3D urban design, TOD, public space vitality, human scale