A train protection system automatically applies the brakes of a train if the speed limit for a segment of track is exceeded or if the train enters a track segment that is currently signalled with a red light (i.e., the segment should not be entered). Giving reasons for your answer, chose a reliability metric that might be used to specify the required reliability for such a system.

There are two essential safety requirements for such a system:
■ The train shall not enter a segment of track that is signalled with a red light.
■ The train shall not exceed the specified speed limit for a section of track.
Assuming that the signal status and the speed limit for the track segment are transmitted to on-board software on the train before it enters that track segment, propose five possible functional system requirements for the on-board software that may be generated from the system safety requirements.