derail indicator

例句：

1. 1. The train's derail indicator was triggered by asudden jolt.
   火车的脱轨指示器被突然的震动触发了。
2. 2. Theengineer monitored the derail indicator closely duringthe crossing.
   工程师在过河时密切监控脱轨指示器。
3. 3. Thederail indicator is anessential safety feature on many railwaysystems.
   许多铁路系统中，脱轨指示器是一个重要的安全特性。