Part of a railway signalling system, a train stop, trip stop or tripcock is a train protection device that automatically stops a train if it attempts to pass a signal when the signal aspect and operating rules prohibit such movement, or if it attempts to pass at an excessive speed.

The 1995 Russell Hill subway accident was a deadly train crash that occurred in Toronto, Ontario, Canada, on Line 1 Yonge–University of the Toronto subway on August 11, 1995. Three people were killed and 30 were taken to hospital with injuries when one train rear-ended another train. The subway line was shut down for five days following the incident. Investigations found that human error and a design flaw in the mechanical safety devices caused this accident. It remains the deadliest accident in a rapid transit system in Canadian history.