两组两个电子回路在信号前设置在轨道上黑桃最有可能使火车有发生碰撞的危险。当Visual indication passed to a train driver to advise the speed, direction or route of the train. There are almost as many types of signals as there are railways but they fall into the following main categories:1) handsignals - used mainly where there are no fixed signals or where the fixed signalling has failed. 2) semaphore signals - a fixed lineside signal where the stop indication is displayed as a horizontally positioned arm and proceed as a 45º or vertical arm. 3) colour light signal - a fixed lineside signal showing light indications to drivers. 4) cab signals - where the indications are displayed in the driver's cab.
" class="glossaryLink ">信号它是红色的并发射电磁场。当列车上的天线探测到第一个天线发射的磁场时环在一对中，它启动一个电子计时器。该对的第二个循环发射的场停止计时器。遇到的第一对环路被隔开，以便列车上的计时器可以计算是否超过接近信号机的安全速度。如果是，制动器将自动接合。第二对环路距离信号较近，且放置得非常近，因此安全速度实际上为零。TPWS将与现有AWS一起使用。
