在城市承办重大活动等特殊时期需要加强地铁安检措施防范恐怖袭击。本文分析了特殊时期地铁安检增加手持金属探测仪环节的实施效果，并与常态地铁安检措施进行比较。首先，构建了常态地铁安检和特殊时期地铁安检的优化模型。其次，对比不同情境下手持金属探测仪和X射线安检仪等安检措施对于潜在袭击者的威慑、对普通乘客的出行便利性、社会福利的影响。最后进行重要参数敏感性的数值分析。研究表明，特殊时期地铁安检增加手持金属探测仪环节后，可以降低物检环节X射线安检仪的最优检测精度要求，从而为普通乘客提供更多便利；但是常态安检X射线安检仪具有更高的检测精度，能够以更大概率识别出潜在袭击者；只有在满足特定条件下，特殊时期采取地铁安检强化措施才能够提高整体的社会福利。

Subway security inspection should be improved during some important periods when cities take over important events. In this paper social welfare effects of reinforced subway security inspection during the special period are analyzed, and then they are compared with those of the universal subway security inspection. In general, a passenger maybe a potential attacker or a normal passenger. Because of the limits of technology, the checking accuracy of X-ray checking machine for screening potential attackers is highly correlated with the false alarm rate for normal passengers. Thus, the optimal security inspection accuracy of checking machine needs to be analyzed. First, we summarizes the management characteristics of the universal and special subway security inspection processes are summarized. In the special security inspection, every of passengers must be accepted extra checking used the hand-held metal detector. Accordingly, the expected social welfare of the universal subway security inspection can be expressed as: SW^M=(1-t)·(V-P_F^M·(C_A+C_N))+t·(P_D^M·(d-C_A)-d), where t is the proportion of the potential attackers; P_D^F is the checking accuracy of X-ray checking machine for screening potential attackers; P_F^M is the false alarm rate of X-ray checking machine for screening universal passengers; V is the universal passengers' social welfare because of security inspection; C_N is the universal passengers' time cost because of extra artificial checking; C_A is the artificial checking cost; and d is the damage of terrorist attack. Similarly, the expected social welfare of the special subway security inspection can be expressed as: SW₁^M=(1-t)·[V-C_A-C_N-(C_A+C_N)·P_F^M1]+t·[(1-θ)(d-C_A)·P_D^M1-(1-θ)d-(1+θ)C_A], where θ is the proportion that potential attackers carry hazardous material with them, and the superscript 1 represents the special security inspection. Second, we discuss the different effects of the hand-held metal detector and the X-ray screening instrument on deterrence of potential attackers, convenience of universal passengers, and social welfare. In particularly, the accuracy of X-ray checking machine is measured as P(attacker alarm), where a higher value for this probability implies a greater deterrence for attackers. Similarly, the inconvenience effect for normal passengers is measured as P(inspect normal passenger), where a higher numerical value implies a greater inconvenience of normal passenger. Last, we make the numerical analysis about the impact of hand-held metal detector. Thus, we can get the following conclusions. Compared with the universal subway security inspection, the accuracy of X-ray checking machine can be reduced in the special case, in order to reduce the false alarm rate and inconvenience for normal passenger. Because the accuracy of X-ray checking machine in the universal subway security inspection is higher, it can effectively screen the potential attackers with the larger probability. However, only under some special conditions, the extra strengthening measures of subway security inspection, such as the hand-held metal detector, can improve total social welfare in the special subway security inspection. Thus, it is necessary to improve hardware devices according to some scenarios. The study provides some management measures for subway security.