Abstract: Rail transit faces several new problems and challenges while bringing positive effects to cities' traffic, economic, and social development. With the increase in line density, the number of rail transit passengers increases quickly, which often causes space safety hazards in evacuation, firefighting, and emergency events. It is urgent to form effective space countermeasures against the risks. Systematic and refined identification, screening, diagnosis, and optimization of practical critical spatial operating conditions and hidden areas in rail transit have become important technical directions for high-quality urban spatial development. 
　　To cope with the pressure of matching passenger flows, which frequently fluctuate or even increase, this study analyzed high-density, quick-growing, and low-speed passenger flows in railway stations with different sizes, different surrounding businesses, and different usage objects. The spatial and temporal evolutionary characteristics of high-density and quick-growing passenger flows were summarized, such as "fast is slow", "natural channelization", and "pendulum effect". Two quantitative indexes of "sectional relative passenger density" and "passenger flow growth" were established to recognize occurrence time nodes of high-density and quick-growing passenger flows. These provide a feasible method and an essential premise for recognizing and preventing high-density and quick-growing passenger flows.
　　The railway station-city connection space includes spatial sequences with diversified forms, interleaving flow lines and complicated elements from ground entrance and exit of rail transit to gates in the payment area of the station hall. It is a transfer area between the internal station hall and the urban public space. It may intensify the passenger flow-space conflicts directly if the railway station-city connection space is not set reasonably enough. Hence, it is easy to expose the bottleneck characteristics in coping with the impacts of high-density and quick-growing passenger flows.
　　The Guanyinqiao Station of Chongqing Rail Transit was chosen as the research object in this study. The space evaluation indexes of "adaptability" and "robustness" were built by using the analytic hierarchy process (AHP), Delphi method, and simulation. The comprehensive effectiveness of the railway station-city connection space to cope with high-density and quick-growing passenger flows was evaluated from perspectives of emergency measures and spatial capacity. On this basis, common types of dynamic spatial bottlenecks (bottleneck against local space, bottleneck against variable moving speed, bottleneck against flow line intersection, and bottleneck against crowd retention) and element features were recognized and summarized.
　　To address such common bottlenecks of railway station-city connection space, short-term countermeasures were proposed, such as "access separation", "path integration", "rapid expansion", and "interface reshaping". Combining with technological measures like fabricated buildings, variable structures, and high-performance equipments, the high-density and quick-growing passenger flows during rush hours are evacuated based on space-time dimensions. It provides a new idea to study countermeasures to potential hazards in urban spaces under generalized conditions.

Key words: rail transit, public safety, station entrance, spatial response

摘要： 资源优化配置与运行效率先行驱动下，城市轨道交通规模持续发展。轨道交通站城衔接空间作为客流汇聚、功能衔接、公共安全等层面影响叠加的焦点空间，伴随公共卫生风险对于城市空间的持续侵扰，愈发难以承载频繁波动的客流冲击，尤以客流量数倍于平时且持续增长，呈现高密聚集、低速流动特征的高密疾增客流为主。以空间安全为导向，以早期预防机制为思路，以高密疾增客流时空特征为切入点，通过可变性构造的技术干涉，并以观音桥站作为空间载体阐述轨道交通站城衔接空间针对安全隐患预防层面的系列应变优化对策。

关键词: 轨道交通, 公共安全, 站点出入口, 空间应变