22-07-2014, 08:04 PM
For Preventing head-on collisions there are several different cases (in no particular order):
[and assuming you're thinking about areas controlled by Track Circuit Block]
1) signalled moves from controlled signals - prevented by opposing locking from setting the second route;
2) bidirectional Auto sections - generally some form of additional locking such as a direction switch;
3) Train running away from sidings/depot/freight yard etc - we use trap points to direct the run-away train away from the main/passenger line;
4) where one of the trains is overrunning;
a. TPWS will mitigate this by applying the brakes in the overrunning train. TPWS is not fail-safe but having said that has proved itself reliable and is designed to stop an overrunning train before a collision point.
b. Flank protection may be provided by calling points which are not in the route to a position which protects the route, It's limited because you don't want to prevent valid parallel moves.
c. Swinging overlaps may be called to a preferred position in order to direct an overrunning train in a particular direction.
5) where both the trains have overrun: current UK Principles explicitly state that this situation is not considered when designing controls, however, any of the points under (4) above would apply individually to each train.
[and assuming you're thinking about areas controlled by Track Circuit Block]
1) signalled moves from controlled signals - prevented by opposing locking from setting the second route;
2) bidirectional Auto sections - generally some form of additional locking such as a direction switch;
3) Train running away from sidings/depot/freight yard etc - we use trap points to direct the run-away train away from the main/passenger line;
4) where one of the trains is overrunning;
a. TPWS will mitigate this by applying the brakes in the overrunning train. TPWS is not fail-safe but having said that has proved itself reliable and is designed to stop an overrunning train before a collision point.
b. Flank protection may be provided by calling points which are not in the route to a position which protects the route, It's limited because you don't want to prevent valid parallel moves.
c. Swinging overlaps may be called to a preferred position in order to direct an overrunning train in a particular direction.
5) where both the trains have overrun: current UK Principles explicitly state that this situation is not considered when designing controls, however, any of the points under (4) above would apply individually to each train.