TPWS Zero

[Lufcman]

Can anyone explain exactly the difference between TPWS and TPWS Zero?

 

[Trackman]

This might explain it, if I think what your interpretation of TPWS zero is.
From network rail:

Safety Central – Network Rail

safety.networkrail.co.uk

Two sets of two electronic loops are set in the track before signals where a SPAD would be most likely to put a train into risk of being involved in a collision. The loops are energised when the signal is red and emit electromagnetic fields. When an antenna on the train detects the field emitted by the first loop of a pair it starts an electronic timer. The field emitted by the second loop of the pair stops the timer. The first pair of loops encountered are spaced so that the timer on the train can calculate whether the safe speed for approaching the signal is being exceeded. If it is, the brakes are automatically applied. The second pair of loops are situated closer to the signal and are placed very close together such that the safe speed is effectively zero.

 

[Railsigns]

TPWS(0) is a specific type of TPWS fitment that can be used to reduce the start-away risk at a platform starting signal. It involves the provision of one or more "OSS(0)"s at the car stop marker positions (on approach to the signal). If the platform is on a through line, the OSS(0)s are de-energised when a train is signalled towards the applicable signal, and re-energised when the train is timed to a stand. "(0)" refers to the set speed being zero.

 

[swt_passenger]

TPWS(0) is a specific type of TPWS fitment that can be used to reduce the start-away risk at a platform starting signal. It involves the provision of one or more "OSS(0)"s at the car stop marker positions (on approach to the signal). If the platform is on a through line, the OSS(0)s are de-energised when a train is signalled towards the applicable signal, and re-energised when the train is timed to a stand. "(0)" refers to the set speed being zero.

So would there be many different grid positions in a long terminus platform so that if a variety of short trains could be at the buffers it would always prevent taking a run up towards the starting signal? I’m thinking of Waterloo as an example with its many permutations of 5 types of EMU and various lengths of 158/159 in multiple.

 

[Railsigns]

So would there be many different grid positions in a long terminus platform so that if a variety of short trains could be at the buffers it would always prevent taking a run up towards the starting signal?

Potentially there could be many different loop positions, but fewer loops may be needed where the distance from the signal to the conflict point is longer.

 

[swt_passenger]

Potentially there could be many different loop positions, but fewer loops may be needed where the distance from the signal to the conflict point is longer.

Thanks. I suppose if there’s anywhere that would have short distances to points of conflict off the platform end it would possibly be much of Waterloo?

 

[zwk500]

Thanks. I suppose if there’s anywhere that would have short distances to points of conflict off the platform end it would possibly be much of Waterloo?

Yes and no. The distance to the first absolute conflict is very short, but because of the multitude of routes possible by using flank protection you can increase the distance to the actual conflict when required. Also, at Waterloo a mid-platform grid would be able to stop trains before the signal even if they had had a bit of a run up to 5/10mph. So you wouldn't necessarily need a grid for every possible combination, just 2 or maybe 3 positions.

 

[swt_passenger]

Yes and no. The distance to the first absolute conflict is very short, but because of the multitude of routes possible by using flank protection you can increase the distance to the actual conflict when required. Also, at Waterloo a mid-platform grid would be able to stop trains before the signal even if they had had a bit of a run up to 5/10mph. So you wouldn't necessarily need a grid for every possible combination, just 2 or maybe 3 positions.

Thanks for adding the extra detail.

 

[zwk500]

Thanks for adding the extra detail.

Just a quick disclaimer - I have no idea if Waterloo does have flank protection as I've described it. I've also got no idea how many TPWS 0 grids Waterloo has, if any.

 

[CAF397]

I think Manchester Airport has TPWS(0) grids.

 

[AJD]

Since they rebuilt King's Cross, I've often sat there wondering why there is an additional set of loops prior to the starting signal (which is already fitted with its own TSS). Sounds remarkably similar to the above. Another learning day!

 

[Efini92]

I think Manchester Airport has TPWS(0) grids.

I always wondered what those OSS were for

 

[swt_passenger]

Just a quick disclaimer - I have no idea if Waterloo does have flank protection as I've described it. I've also got no idea how many TPWS 0 grids Waterloo has, if any.

Ah, it’s actually explained for Waterloo in the ‘wordy bits’ of the online sectional appendix. They are fitted 32m from the signal, on platforms 1-9, and 20, 21 and 22. That’s after an amendment in Aug 2017, so coincides with the last remodelling. Is it likely that the work done on P1-9 has meant the latest standards have had to be applied? Also that the layout of the former international throat, which is also recent work, must mean there’s more risk in those 3 platforms than the other 2?

 

[CAF397]

I always wondered what those OSS were for

When Manchester Airport station was at its capacity, would always end up with the cab over them if put in permissively!

 

[Bald Rick]

So would there be many different grid positions in a long terminus platform so that if a variety of short trains could be at the buffers it would always prevent taking a run up towards the starting signal? I’m thinking of Waterloo as an example with its many permutations of 5 types of EMU and various lengths of 158/159 in multiple.

Two is normally the maximum. One on the signal, and another to catch an 8 car starting away from the stops, (which would also catch any other, shorter train)