How widepread is TPWS?

[rich r]

I've done a bit of searching but don't seem to able to find much information on how widely deployed TPWS is? Generally on my daily commute I see AWS everywhere, but only see TPWS grids around main lines and cities.

So what I was wondering how widespread TPWS was in general? Is it restricted to only lines over a certain speed or traffic level, or is it just a case of the budget for installation hasn't been found for installing it on all lines?

 

[TheEdge]

Its pretty much universal. Not all signals and all locations have it but you would struggle to find any passenger carrying lines not fitted in some manner.

 

[Joseph_Locke]

I've done a bit of searching but don't seem to able to find much information on how widely deployed TPWS is? Generally on my daily commute I see AWS everywhere, but only see TPWS grids around main lines and cities.

So what I was wondering how widespread TPWS was in general? Is it restricted to only lines over a certain speed or traffic level, or is it just a case of the budget for installation hasn't been found for installing it on all lines?

TPWS is fitted (or not) based on risk, which is function of likelihood (number of trains approaching an adverse aspect) and consequence (distance from signal to point of conflict, modified by approach speed). This means that freight only lines often don't get TPWS because the speed and risk to life is very low.

On passenger lines signals that just protect the train ahead (in the same direction) don't get TPWS, but junction signals and large drops in permissible speed generally do.

 

[MarkyT]

On passenger railways, all signals protecting junctions with crossing or merge conflicts are fitted if the layout doesn't already provide flank protection. A standard fitment at a signal consists of a trainstop at the signal and an overspeed about 300 to 400m on approach. Some signals on higher speed lines also have TPWS+ which adds an additional overspeed installation at typically around 700m from the signal. Exits from freight lines and sidings onto passenger lines are always trapped to throw an unauthorised movement clear of the passenger lines (not always successfully in practice!) so they do not usually have TPWS. Signals protecting junctions that are divergent only do not have TPWS unless other reasons require it. Miniature overspeed loops are always fitted on approach to bufferstops on passenger line. Every installation is risk assessed and sometimes plain line signals protecting platforms are fitted if the risk score is high enough. Risk is calculated using a formula that takes into account type and speed of trains, traffic density and loading. There's another recent thread discussing criteria for application at speed restrictions: http://www.railforums.co.uk/showthread.php?p=3124904

 

[rich r]

Thanks for those replies, that does add some insight.

For example, heading east of Leeds towards Selby/Hull there are TPWS grids up to and including Neville Hill, but nothing after that. This is also the limit of electricification.

I guess there are few junctions (other than Micklefield and Hambleton), and reasonably large gaps between trains in the same direction (the traffic being primarily 70mph DMU or freight).

 

[HarleyDavidson]

On passenger railways, all signals protecting junctions with crossing or merge conflicts are fitted if the layout doesn't already provide flank protection. A standard fitment at a signal consists of a trainstop at the signal and an overspeed about 300 to 400m on approach. Some signals on higher speed lines also have TPWS+ which adds an additional overspeed installation at typically around 700m from the signal. Exits from freight lines and sidings onto passenger lines are always trapped to throw an unauthorised movement clear of the passenger lines (not always successfully in practice!) so they do not usually have TPWS. Signals protecting junctions that are divergent only do not have TPWS unless other reasons require it. Miniature overspeed loops are always fitted on approach to bufferstops on passenger line. Every installation is risk assessed and sometimes plain line signals protecting platforms are fitted if the risk score is high enough. Risk is calculated using a formula that takes into account type and speed of trains, traffic density and loading. There's another recent thread discussing criteria for application at speed restrictions: http://www.railforums.co.uk/showthread.php?p=3124904

They're also fitted at certain locations protecting level crossings, Bedhampton and Cosham are two such locations, which means that you have to approach the signal/platform at <10 mph, which can be highly irritating especially when you have passed the previous signal on a single yellow, only to come around the corner to find the crossing down and signal off.

 

[Skoodle]

On passenger lines signals that just protect the train ahead (in the same direction) don't get TPWS, but junction signals and large drops in permissible speed generally do.

Except for the new East London Line. When it was rebuilt every signal has Train Stop loops and about 75-80% of them have OS loops. To be fair though I think they just thought go with everything, opened with GSM-R off the bat in 2010 and PoSAs also.

 

[MichaelAMW]

They're also fitted at certain locations protecting level crossings, Bedhampton and Cosham are two such locations, which means that you have to approach the signal/platform at <10 mph, which can be highly irritating especially when you have passed the previous signal on a single yellow, only to come around the corner to find the crossing down and signal off.

Are you saying that there are situations where, in the absence of TPWS, you would approach a red signal or platform (or perhaps both if there is a level crossing just beyond) in a particular cautious way, e.g. I'm thinking of other threads where there is a rule about passing the AWS magnet at 15 or 20, but you end up being "scared" of the TPWS grids and approach more slowly than really you need to?

 

[MichaelAMW]

On passenger railways, all signals protecting junctions with crossing or merge conflicts are fitted if the layout doesn't already provide flank protection. A standard fitment at a signal consists of a trainstop at the signal and an overspeed about 300 to 400m on approach. Some signals on higher speed lines also have TPWS+ which adds an additional overspeed installation at typically around 700m from the signal.

Does that mean in practice the overspeed grids for a particular red signal can be *before* the previous signal displaying single yellow?

 

[MarkyT]

Does that mean in practice the overspeed grids for a particular red signal can be *before* the previous signal displaying single yellow?

I don't think there are any like that, but I could be wrong. I'm sure it can get complex if there are additional closing up signals on approach to a station with special aspect sequences. Places like Woking spring to mind where the signalling is trying to cope with very high frequency for the majority of stopping services as well as high through speed for a few non stoppers. In general with higher line speeds signals are further apart.

 

[Railsigns]

Does that mean in practice the overspeed grids for a particular red signal can be *before* the previous signal displaying single yellow?

Yes; I've known that to occur.