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 the track segment, propose five possible functional system requirements for the onboard software that may be generated from the system safety requirements.

Question

There are two essential safety requirements for the train protection system:
• The train shall not enter a segment of track that is signaled with a red
light.
• The train shall not exceed the specified speed limit for a section of track.

Answer 1

There are several different possibilities here. Some examples:
1. The system shall ensure that the train brakes are applied when a 'red signal'
is received.
2. The system shall sound an alarm in the driver's cabin when a 'red signal' is
received.
3. The system shall compare the train speed with the segment speed limit once
per second.
4. If the train speed exceeds the segment speed limit and the train throttle
position is not zero then the throttle position should be reset to zero.
5. If the train speed exceeds the segment speed limit and the train deceleration
is less than the comfortable decleration limit then the train brakes should be
applied.