Metric Railway

[Trog]

Remember we are talking about the railway here, it would not be beyond the realms of possibility for the S&T and operating to go metric at the same time as the P-Way decide to standardise on the cubit.

You may find that speedos and speed signs go metric and track measurement stays imperial using the existing mileposts. As despite what the keen young things on here think about super wizzo digital surveys, actually checking and converting all the records would be a horrendous task. A lot of that checking would have to be done on site by quite senior people. Unless you want the new records to be worse than the existing, as they are the only people with the depth of experience to do it.

 

[Up_Tilt_390]

Remember we are talking about the railway here, it would not be beyond the realms of possibility for the S&T and operating to go metric at the same time as the P-Way decide to standardise on the cubit.

You may find that speedos and speed signs go metric and track measurement stays imperial using the existing mileposts. As despite what the keen young things on here think about super wizzo digital surveys, actually checking and converting all the records would be a horrendous task. A lot of that checking would have to be done on site by quite senior people. Unless you want the new records to be worse than the existing, as they are the only people with the depth of experience to do it.

What do you do for a living that gives you this knowledge. Have you worked in railway engineering before? Is so, what about did you do?

 

[furnessvale]

Remember we are talking about the railway here, it would not be beyond the realms of possibility for the S&T and operating to go metric at the same time as the P-Way decide to standardise on the cubit.

You may find that speedos and speed signs go metric and track measurement stays imperial using the existing mileposts. As despite what the keen young things on here think about super wizzo digital surveys, actually checking and converting all the records would be a horrendous task. A lot of that checking would have to be done on site by quite senior people. Unless you want the new records to be worse than the existing, as they are the only people with the depth of experience to do it.

That's strange. As a junior per way engineer in the mid to late 1960s I was using metric measurements. Electrification of the WCML from Weaver Jcn to Glasgow was laid out using metric.

Existing mileposts were picked up in the longitudinal surveys......and they were inaccurate!

 

[Radedamer]

Would metric speedometers and imperial speed limit signs (or vice versa) actually matter? They're pretty common on roads, after all, when vehicles cross borders (often in large numbers eg between USA and Canada) or countries switch systems.
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Would metric speedometers and imperial speed limit signs (or vice versa) actually matter? They're pretty common on roads, after all, when vehicles cross borders (often in large numbers eg between USA and Canada) or countries switch systems, so I would have guessed that railways, with more controlled, less variable, environments, restricted access and – crucially – better trained drivers, would have coped with this difference.

 

[DerekC]

Would metric speedometers and imperial speed limit signs (or vice versa) actually matter? They're pretty common on roads, after all, when vehicles cross borders (often in large numbers eg between USA and Canada) or countries switch systems, so I would have guessed that railways, with more controlled, less variable, environments, restricted access and – crucially – better trained drivers, would have coped with this difference.

Railway speed restrictions are more critical than road ones because they show the maximum speed on a curve - if you exceed this by a significant amount the train may derail. The safe way round (I guess) is to have km/h on the speedo and miles per hour on the track signs - at least that way you will be going too slowly rather than too fast - but Murphy's law will apply and sooner or later a driver will be driving a mph train when yesterday he was in a km/h train and try to go through a 50 mph curve at 80. So let's have matching displays and signs. Of course as and when ERTMS comes in we won't need PSR signs anyway, so the job gets easier.

 

[Railsigns]

Of course as and when ERTMS comes in we won't need PSR signs anyway, so the job gets easier.

The Cambrian Line, which has ERTMS, is littered with PSR signs (metric). Admittedly, these are only provided for degraded working, but nevertheless they exist.

 

[furnessvale]

Railway speed restrictions are more critical than road ones because they show the maximum speed on a curve - if you exceed this by a significant amount the train may derail. The safe way round (I guess) is to have km/h on the speedo and miles per hour on the track signs - at least that way you will be going too slowly rather than too fast - but Murphy's law will apply and sooner or later a driver will be driving a mph train when yesterday he was in a km/h train and try to go through a 50 mph curve at 80. So let's have matching displays and signs. Of course as and when ERTMS comes in we won't need PSR signs anyway, so the job gets easier.

I think you are underestimating the route knowledge required of a train driver as opposed to road.

When a train driver actually sees the sign indicating the authorised speed, if he is not actually doing that speed it is FAR too late to adjust it.

Speed limit signs on UK railways are not meant as an instantaneous indicator, rather they are a daily reminder of the speed limit.

 

[DerekC]

I think you are underestimating the route knowledge required of a train driver as opposed to road.

In what way do you think I am underestimating the need for route knowledge? Did you mean in saying that we won't need PSR signs when ERTMS comes in?

 

[edwin_m]

I think you are underestimating the route knowledge required of a train driver as opposed to road.

When a train driver actually sees the sign indicating the authorised speed, if he is not actually doing that speed it is FAR too late to adjust it.

Speed limit signs on UK railways are not meant as an instantaneous indicator, rather they are a daily reminder of the speed limit.

In principle yes. However signs requiring a reduction in speed by more than a certain amount are required to have warning signs (triangular with yellow border) placed at braking distance on the approach.

Drivers route knowledge still comes into play, but speed restriction signs are now also considered as safety critical on the "belt and braces" principle.

Permitted speeds on curves are set to give a comfortable ride for passengers, and probably also to minimise wear and tear if trains routinely went round at higher speeds. The speed at which there is a risk of derailment is considerably higher than the posted limit. Hence for the smaller speed reductions that don't require warning signs, there is little danger if the driver brakes too late. See for example a recent incident near Peterborough on the RAIB website where a 25mph connection was taken at about twice that speed. It was no doubt very uncomfortable and a couple of people on board had minor injuries but the train kept to the rails.

 

[furnessvale]

In what way do you think I am underestimating the need for route knowledge? Did you mean in saying that we won't need PSR signs when ERTMS comes in?

My next two sentences explained that. The knowledge of a certain speed limit is already in the drivers head. The fixed sign is simply a daily reminder AFTER the event. Any driver relying on the fixed signs would come to grief at the first restriction, and yes, the retention of fixed signs would be essential after ERTMS to assist drivers in retaining their route knowledge for emergencies.

 

[DerekC]

My next two sentences explained that. The knowledge of a certain speed limit is already in the drivers head. The fixed sign is simply a daily reminder AFTER the event. Any driver relying on the fixed signs would come to grief at the first restriction, and yes, the retention of fixed signs would be essential after ERTMS to assist drivers in retaining their route knowledge for emergencies.

I (very politely) suggest that you should take a fresh look at what ERTMS looks like from a driver's perspective. As the train approaches a speed restriction the driver will be warned and supervised in slowing down to the reduced speed on the in-cab display, so no need for speed boards and no possibility of exceeding the set speed. And in an emergency (presumably if ERTMS fails) the train would be running at slow speed anyway. So don't let's waste money on speed boards that we won't need. Of course all this only applies when all trains on a route are ERTMS fitted and progress over the past 15 years suggests that I will be pushing up daisies by then!

 

[furnessvale]

In principle yes. However signs requiring a reduction in speed by more than a certain amount are required to have warning signs (triangular with yellow border) placed at braking distance on the approach.

Drivers route knowledge still comes into play, but speed restriction signs are now also considered as safety critical on the "belt and braces" principle.

Permitted speeds on curves are set to give a comfortable ride for passengers, and probably also to minimise wear and tear if trains routinely went round at higher speeds. The speed at which there is a risk of derailment is considerably higher than the posted limit. Hence for the smaller speed reductions that don't require warning signs, there is little danger if the driver brakes too late. See for example a recent incident near Peterborough on the RAIB website where a 25mph connection was taken at about twice that speed. It was no doubt very uncomfortable and a couple of people on board had minor injuries but the train kept to the rails.

Having been a permanent way engineer for a number of years before changing career, I am aware of the mechanisms surrounding speed on curves.

Whether a train stays on the line or derails at excessive speed is entirely due to the cant deficiency it is suffering at the time. Some cant deficiency is already used by fast passenger trains on mixed traffic lines which is why the passenger gets the feeling of being thrown outwards. Tilting trains may reduce the sensation for the passenger but do nothing to reduce the cant deficiency forces in play for the track and the train.

It is some years since I was active in this field so, without digging the books out, allowable cant deficiency is around 100mm for a non tilting train, and derailment occurs around 275-300mm but I stand to be corrected on the current allowances.

 

[craigybagel]

The example I was shown it just restricted the power available and I don't think there was any brake intervention. A bit like a cars rev limiter.

It wasn't 158834 by any chance was it? It's been fitted with a 4 speed transmission as a trial and apparently the way its been designed with the gearing it runs out of power at 90mph.

Sorry to disappoint, but the version of ERTMS which is to be rolled out in GB (unlike the earlier one used on Cambrian) now allows for the driver display to be either in metric or imperial units, controlled by a software "switch" set by a variable transmitted from the infrastructure. So we can use miles for as long as we like and then switch to kilometres, or even have some routes in each unit, with the train display switching from one to the other as it crosses the boundary.

I had wondered if that would be the case, given that the 158s already run on MPH when they're on ERTMS level 0 (Running on conventional lines, the screen still shows an mph speedometer and the brakes will still kick in at some point over 90 I believe, or 75 if coupled to a slower unit).

 

[notadriver]

A 4 speed transmission ? The 172s use a 6 speed Eco-life ZF

 

[cjmillsnun]

Remember we are talking about the railway here, it would not be beyond the realms of possibility for the S&T and operating to go metric at the same time as the P-Way decide to standardise on the cubit.

You may find that speedos and speed signs go metric and track measurement stays imperial using the existing mileposts. As despite what the keen young things on here think about super wizzo digital surveys, actually checking and converting all the records would be a horrendous task. A lot of that checking would have to be done on site by quite senior people. Unless you want the new records to be worse than the existing, as they are the only people with the depth of experience to do it.

Yes the cost is horrendous, but the long term cost benefits are larger. I've a lot of experience (11 years) with digitising an asset record of similar age to the railways. Most of it can be done at the time of renewal by reasonably junior staff (with decent modern surveying grade kit). We're not talking about an overnight thing, but something that would take place over a couple of decades. It probably is already happening and is already in an advanced state.

 

[Trog]

Yes the cost is horrendous, but the long term cost benefits are larger. I've a lot of experience (11 years) with digitising an asset record of similar age to the railways. Most of it can be done at the time of renewal by reasonably junior staff (with decent modern surveying grade kit). We're not talking about an overnight thing, but something that would take place over a couple of decades

The trouble with that is that it is the old stuff you most need to know about.

For track alone survey on renewal would probably take forty years to get near complete coverage on the mainlines, and nearly a century for the more minor branches. The surface geometry you seem to be talking about is also the easy bit, I have yet to see a survey instrument that can identify all the different types of sleeper while they are buried in ballast. Or a video system with built in wire brush and stick of chalk to read the rail age and section data.

 

[craigybagel]

A 4 speed transmission ? The 172s use a 6 speed Eco-life ZF

Yup, 4 speed Voith DIWA transmission. Not worked it for a while though so I dont know if it's still got it, but hopefully it does and they fit it to the others - compared to its siblings it goes like excrement off a bladed gardening implement.