## 4 Case Studies Based on Real Data
### The Influence of Widening the Exit on Economic Cost  
Figure 6(a) shows the current video surveillance footage, with blue boxes representing the monitoring area (dangerous area). As seen, as the camera devices are affected by factors such as camera resolution and lighting, a set of surveillance equipment can only effectively recognize within a distance of about 50 m, which requires installing a set of monitoring equipment at regular intervals and incurs high costs (red boxes in Figure 6(b)). According to the proposal in this paper to define part of the platform outside the bottleneck area as the monitoring area, monitoring and warning this area can effectively achieve the goal of preventing passengers from falling from the platform. By alleviating congestion, the frequency of passengers entering the monitored (danger) area is correspondingly reduced. The remaining risk area that passengers still enter is redefined as the new monitoring area. Therefore, we narrow the monitoring area and redefine part of the platform outside the bottleneck (Figure 8) as the danger area for video surveillance (monitoring area). Passengers entering this area will be monitored in real-time, and an alarm will be triggered if they remain there for more than 3 s (red boxes in Figures 6(a) and 8). A comparison in Figures 8 and 9 shows that the monitoring area is significantly reduced. The reduced monitoring area cuts down the number of required monitoring devices (cameras), thereby lowering the monetary costs. Obviously, the new monitoring area is significantly smaller than the current one, resulting in less required surveillance equipment and lower economic costs. Table 9 shows that the new monitoring area is only 80 m\({}^{2}\), cutting down the area by 91% compared to the current one. According to the information provided by the station managers, the cost of a set of monitoring equipment is approximately CNY 50,000. All monitoring equipment  
Figure 6: The exit width with different risk probabilities (based on Table 9 using Python 3.7). Figure 7: The current monitored area and surveillance devices (red boxes) (actual operational pictures provided by the station): (**a**) A passengers entering dangerous areas; (**b**) surveillance camera. 1. We found that the current exit width of 6 m is insufficient in ensuring congestion-free passenger flow, contributing to the annual platform fall incidents in China. We recommend increasing the platform exit width to a range of 6.43 to 7.01 m to reduce the risk probability to 10%. This adjustment also decreases the likelihood of passengers entering hazardous zones, allowing for a redefinition of monitoring areas outside the bottleneck. 2. Compared to the previous design, the newly defined monitored areas are reduced by 91%, resulting in a 77.7% decrease in the required surveillance equipment and a 50% reduction in monetary investment. 3. Due to the restriction of a typical platform width of 10 m, the limit of redesigning the exit width aims to allow 2770 passengers to leave the platform within the maximum specified travel time. At this time, the risk probability is still 3.1%. 4. Based on actual operational constraints, it is necessary to set a minimum risk tolerance (risk probability) for station managers. The ranges of exit widths required to achieve different aims of risk probabilities vary. 5. Our recommendations provide theoretical guidance for redesigning the platform (exit). However, due to the complexity of the investment plan and approval involved in the renovation of the platform, the width of the exit will remain unchanged in the short term. It is recommended to add managers in bottleneck areas to assist passengers in safely exiting the platform and prevent them from falling down onto the tracks during extreme passenger flows. Fortunately, the suggested expansion of the exit width to 6.43 m has at least been implemented in several high-speed railway stations in China, receiving positive feedback from station managers.