PartⅢ Passage
Metro Signal
Signaling and operation on metro system involves train control，train signal，signage and train length，etc.
Today，metro train control is done by an Automatic Train Control system（ATC），which is a combination of three sub-systems，ATO，ATP and ATS.ATP separates train，ATS routes trains，and ATO gathers information from both ATS and ATP to directly control the trains.
The metro signaling lights work just like traffic lights for cars.Red means stop，and green means advance.The signaling lights are automatically controlled by the location of the trains.As one of the trains moves along the track，it relays on the track to send the signal of its location to the lights.A red light stays on until a leading train has moved a safe distance.
Before，metros ran four-car and six-car trains.However，there are no more four-car trains used in the system after year 2000.Even eight-car trains are in service nowadays.The train's length decides the safe distance programmed in the metro signal system.
New Words and Expressions
地铁信号
地铁系统的发出信号和操作控制涉及列车控制、列车信号、标志和列车长度等。
如今，地铁列车控制是通过一个自动列车控制系统（ATC）完成，它组合了三个子系统：ATO、ATP和ATS。ATP保持列车距离，ATS安排列车路线，ATO收集ATS和ATP的信息来直接控制列车。
地铁信号交通灯的功能就像汽车交通信号灯一样。红色意味着停止，绿色意味着行驶。信号灯由列车的位置自动控制。当一列列车沿着轨道行进，它依靠轨道发送自身的位置来控制信号灯。红灯持续长亮直至前方的列车移动至一个安全的距离。
之前，地铁运行4节车厢或6节车厢。然而，在2000年以后，地铁系统没有再使用4节车厢编组的列车，现在甚至有8节车厢的列车投入使用。列车的长度决定了地铁信号系统编程中列车的安全距离。