When do Sheffield TramTrains need TOPS codes to use Network Rail but LU do not?

[edwin_m]

LU are paying for the signalling system so LU can provide whatever train protection they deem fit!

TPWS would probably be easier and cheaper for LU to maintain. No moving parts.

 

[Domh245]

TPWS would probably be easier and cheaper for LU to maintain. No moving parts.

Would have also had the benefit of (probably) being able to use the same techniques as used on the district line shared sections in terms of talking between TPWS and the CBTC system even though they're polar opposites in terms of system function

Although, as I type that it dawns on me that there's also plenty of cases where the CBTC has to 'talk' with tripcock systems where the SSL lines share tracks with the Piccadilly line, so not exactly a big issue and they'll have plenty of train stops for a good few years yet. Will probably make sense to replace it around the same time that Chiltern replace their rolling stock.

 

[edwin_m]

Would have also had the benefit of (probably) being able to use the same techniques as used on the district line shared sections in terms of talking between TPWS and the CBTC system even though they're polar opposites in terms of system function

Although, as I type that it dawns on me that there's also plenty of cases where the CBTC has to 'talk' with tripcock systems where the SSL lines share tracks with the Piccadilly line, so not exactly a big issue and they'll have plenty of train stops for a good few years yet. Will probably make sense to replace it around the same time that Chiltern replace their rolling stock.

I don't think the overlay (NR interlocking controlling SSL TBTC trackside equipment) and underlay (LU interlocking controlling, potentially, TPWS) have much in common.

But TPWS was designed to be easy to interface to existing signaling, essentially intercepting the red lamp and the proving circuit.

Considering how tricky and expensive it is to make any alteration to existing signaling, and that all the Chiltern trains in question have TPWS already, this looks like one of those situations where one body (LU) has reduced its own cost by landing another one (future Chiltern operator) with a bill bigger than the saving.

 

[rebmcr]

I don't think the overlay (NR interlocking controlling SSL TBTC trackside equipment) and underlay (LU interlocking controlling, potentially, TPWS) have much in common. But TPWS was designed to be easy to interface to existing signaling, essentially intercepting the red lamp and the proving circuit. Considering how tricky and expensive it is to make any alteration to existing signaling, and that all the Chiltern trains in question have TPWS already, this looks like one of those situations where one body (LU) has reduced its own cost by landing another one (future Chiltern operator) with a bill bigger than the saving.

I don't see where 3-aspect colour lights, plus tripcocks, is any different than present-day Chiltern operation.

 

[edwin_m]

I don't see where 3-aspect colour lights, plus tripcocks, is any different than present-day Chiltern operation.

It isn't. But Chiltern has to keep a sub-fleet fitted with tripcocks to work. If the opportunity had been taken to install TPWS with re-signalling, Chiltern could dispense with the tripcocks as all their units have TPWS already, could run their entire fleet on the route, and would not have to specify tripcocks for future fleets.

 

[Lewlew]

Only on paper, the reality is that the first train to drop on will be given whatever the next headcode to be used is, with no regard for out of turn working. NR signallers have access to LUL Connect radio systems, so the correct train numbers are always used when required for operational reasons or delay attribution etc.

Bakerloo trains keep their train numbers when on Network Rail, you can see them on opentraintimes maps. They add a letter in front to show the destination. So train 234 running from Queens Park to Harrow will become A234 until reversing in the siding where it becomes M234.

From memory:
J is Stonebridge Park
A is Harrow
M is Queens Park

 

[Mojo]

TPWS would probably be easier and cheaper for LU to maintain. No moving parts.

AIUI, TPWS is not guaranteed to prevent a functioning train being driven at the right speed from passing a signal and prevent it from potentially colliding with another train.

 

[greatkingrat]

Both TPWS and a tripcock apply the emergency brake if a signal is passed at danger. The method of detecting whether a signal has been passed may vary, but the end result is the same. Assuming the signal has sufficient overlap, there is no danger of a collision with either system.

 

[edwin_m]

Both TPWS and a tripcock apply the emergency brake if a signal is passed at danger. The method of detecting whether a signal has been passed may vary, but the end result is the same. Assuming the signal has sufficient overlap, there is no danger of a collision with either system.

Indeed. TPWS is normally fitted to address most but not all of the SPAD risks, but it can be designed to stop a train approaching a red at line speed provided the overlap is long enough. In fact by use of the overspeed sensor the lengthening of an overlap might be less than with a tripcock.

 

[rebmcr]

AIUI, TPWS is not guaranteed to prevent a functioning train being driven at the right speed from passing a signal and prevent it from potentially colliding with another train.

TWPS has two detectors, a designated speed one in advance of the signal, plus a "zero speed" one at the signal itself.

The one in advance protects the overlap, and the one at the signal is the catch-all failsafe.

There is a permutation where the speed sensor is satisfied, but there is just enough momentum at the signal to foul beyond the overlap, which is probably what you are remembering.

 

[Mojo]

TWPS has two detectors, a designated speed one in advance of the signal, plus a "zero speed" one at the signal itself.

The one in advance protects the overlap, and the one at the signal is the catch-all failsafe.

There is a permutation where the speed sensor is satisfied, but there is just enough momentum at the signal to foul beyond the overlap, which is probably what you are remembering.

The difference being, that on Network Rail, overlaps are typically fixed length. Whereas on London Underground, the overlaps are variable, and take into account train speeds, braking capacity, and so on. TPWS does not claim to, and will not, in all cases cause a correctly functioning train being driven at the right line speed, from stopping within the overlap.

Of course, "overlaps" are a part of traditional signalling and not really relevant in this manner for TBTC / CBTC / etc.

 

[D7666]

Specifically - and to be pedantic - on the subject of train radio, some of the terminology used upthread does not really align.

NR radio correctly referred to as GSMR or, more formally GSM[R]. GSMR - however you write it - is the technology, as well as the name.

The equivalent technical term for the LU system is TETRA [Terrestrial Trunked Radio]. There are very good reasons why it was adopted over GSMR too complex to delve into here.

The term LU Connect is really a sort of brand name: Connect is the name used for by the LU comms provider estsablished under PPP [although back in house since last year]. Although LU Connect radio is the official term, it is TETRA technology.

 

[edwin_m]

TWPS has two detectors, a designated speed one in advance of the signal, plus a "zero speed" one at the signal itself.

The one in advance protects the overlap, and the one at the signal is the catch-all failsafe.

There is a permutation where the speed sensor is satisfied, but there is just enough momentum at the signal to foul beyond the overlap, which is probably what you are remembering.

The difference being, that on Network Rail, overlaps are typically fixed length. Whereas on London Underground, the overlaps are variable, and take into account train speeds, braking capacity, and so on. TPWS does not claim to, and will not, in all cases cause a correctly functioning train being driven at the right line speed, from stopping within the overlap.

Of course, "overlaps" are a part of traditional signalling and not really relevant in this manner for TBTC / CBTC / etc.

All true, but there's no reason why the overlap can't be longer so the TPWS always stops the train within it (assuming everything is functioning correctly and the train is within permitted speed). The overlap to achieve this will be no longer and often shorter than the one they will have to fit to do the same thing with a tripcock, because as mentioned TPWS can get the brakes on before the train gets to the signal, but to do that with a tripcock needs some complicated timers.