WCML - Tilt vs Non-Tilt

[ukrob]

The thing is though that pendos only run at 125 if theyre late

Not according to my gps. I commute every day on wcml, if they travel mostly at 125 then they arrive early. If we leave late by say 5_10 mins then we travel at 125 all the way apart from through mk.

Have definitely hit 132mph at one point though

You are wrong on both counts as have been explained. A GPS device (certainly a civilian one) is not accurate enough for you to make these claims.

 

[asylumxl]

You are wrong on both counts as have been explained. A GPS device (certainly a civilian one) is not accurate enough for you to make these claims.

Unless it obtains corrections from the server created by the good folk at OS.
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The GPS sattelites as far as I know just give you the position on the Earth's surface though so where is the elevation data from?

That's what the datums for. If it knows the position of a point and it's height, then it can correct from there on in.

 

[Pumbaa]

You are wrong on both counts as have been explained. A GPS device (certainly a civilian one) is not accurate enough for you to make these claims.

I continually reel from the amazement at the number of folk who take their on-train GPS readings as gospel. I had the misfortune of the timing society on my journey back to Manchester last week, I nearly died of embarrassment for them. 90 in a 75 limit, 45 in a 30 limit, for an entire 2 hours. I was exhausted by the time I alighted

 

[The Planner]

Another one that does the rounds is that HSTs only run at 110 mph between Reading and Swindon unless they are late so that fuel can be saved. I don't know how true this is.

We'd be getting a kicking off the delay minutes if they did, they are certainly timed at 125mph. There isnt enough engineering allowance for them to slack off to that extent.
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Not according to my gps. I commute every day on wcml, if they travel mostly at 125 then they arrive early. If we leave late by say 5_10 mins then we travel at 125 all the way apart from through mk.

Have definitely hit 132mph at one point though

I have that joy too, and believe me, like Pumbaa has explained, you aren't doing 132 and they only slack off for the 110 curves and tunnels. You will arrive Euston early anyway as they have a public differential at the terminus and engineering allowance counts for a lot too.

 

[Zoe]

But if as I am hearing now the GPS can accurately calculate elevation then why would it give an incorrect reading?

 

[asylumxl]

But if as I am hearing now the GPS can accurately calculate elevation then why would it give an incorrect reading?

Depends really if the software is capable of working out speed 3 dimensionally using slope distances. Some software may only be capable of working out 2 dimensional changes. Or it may just have poor intemittent signal.

 

[LE Greys]

In all my experience with GPS, the speed readout is constantly changing, and the unit has an accuracy of 20 m (coincidentally 1 chain). From my experience with stopwatches, an error of 1 chain can throw the result out by several mph, depending on whether you're timing between stations or between quarter miles. Humans tend to have reaction times between 0.1 and 0.25 sec, which creates a far bigger inequality. For proper timing, nothing beats the dynamometer car and its descendants. The stopwatch and the GPS roughly match, and both have advantages and disadvantages. It's awkward having to write down a series of numbers every seven seconds while continuing to look out of the window. Is it possible to run a stopwatch in Excel? Just press Return for every quarter-mile post.

Incidentally, the highest I ever "clocked" on a Pendy was 129, between Acton Bridge and Winsford on the Glasgow-London record run in 2006. Higher than that was a 91 descending Stoke at 133, but that might have been a timing error.

 

[jopsuk]

Speed spikes with GPS are common. Noting this, the World Speed Sailing Council do now accept GPS track data, but the speed taken is the average over a 500m (or longer, depending upon record) distance.

 

[j0hn0]

sorry I don't get 2 of the previous comments at all, I've never heard of "true speed" over ground speed before. GPS receivers are the most accurate way of measuring speed (other than the odometer), on the ground, which is exactly how line speed is measured no?

I find, in the morning and evening peak at least, that the trains that are bang on time, keep a nice smooth, constant 110-118 almost all the way. The train shakes way more doing 125 when we are late

That is entirely my experience, disagree with a proven GPS signal if you will
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We'd be getting a kicking off the delay minutes if they did, they are certainly timed at 125mph. There isnt enough engineering allowance for them to slack off to that extent.
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I have that joy too, and believe me, like Pumbaa has explained, you aren't doing 132 and they only slack off for the 110 curves and tunnels. You will arrive Euston early anyway as they have a public differential at the terminus and engineering allowance counts for a lot too.

yes, only at 1 point though, which was probably a spike as was explained

All other readings are accurate and I don't doubt the planning. I am just saying it as I see it

 

[Zoe]

Ground speed is an aviation term for your speed relative to the surface of the Earth it wasn't a great idea for me to use the term for land based transport as this is always on the ground but the point is that your speed relative to the sufrace of the Earth won't be the same as your true speed unless you are dead level. A GPS device will need to take into account changes in elevation when calculating your true speed. Just dividing distance by time in 2D won't give true speed unless dead level. Some GPS units use a barometirc altimeter rather than GPS data to calculate elevation but again this needs to be taken into account when calculating true speed.

 

[matt]

It depends on the train. On the Siemens EMU stock, the power controller is notched, but it is possible to incrementally increase power, so instead of 20, 40, 60, 80, 100%, you can hold it at 65% by moving the controller carefully.

Bombardier modern stock you definitely can't, and I'm not sure on DMUs. I'm under the impression that it's a no-can-do. I'm not sure on the 390s actually, Respite will tell if he's around.

Don't Pendolinos have a speed hold function?

 

[TGV]

Depends on the GPS unit and how well you know how to use it and interpret the data. I have a Holux GPS data logger, but even the manual for it educates the user into reasons for errors and misreading.

I have crudely calibrated it in the cab and also in my own car. I can vouch for it's general accuracy - of that there is NO DOUBT. It not only confirmed the readings from the train as constant and accurate and that the car was reading 2-4mph fast but it kept the level very constant througout the runs. However, when entering a tunnel or long bridge, the instant data can fluctuate up or down - the manual warns of this, but you can filter these data spikes out in excel afterwards - knowing that a train can't go from 297km/h to 313km/h and down to 298km/h in 3 seconds is a pretty good indication that the 313km/h is an errant figure. However, the unit itself will show on one screen "Average speed" and "Max speed". The Max speed will indeed show 313km/h, leading the uneducated user to conclude this was the fastest speed noted, but once you analyse the graph, it's clear what's going on. Tom Tom type devices will be particularly poor at this kind of simple data interrogation. You need to download the data as a .csv file and analyse it in excel before you can work out real maximums and averages.

Also, if you're on a steel slope, the speed readout won't be accurate - it typically loses accuracy as gradient increases, but we're talking ski-slopes here - in fact, this is one application the device is used for and again, the manual warns against reading too much into instantaneous spikes in data on 30 degree slopes or so. Now, I don't know many railway gradients that are 30 degrees!

So like I said - it depends on the GPS chipset being used, and as with most technology - the person using it. You need to post-process the data afterwards, but once you know what you're doing with the data, it will be as accurate as if you were in the cab writing down thevalue on the speed indicator every 0.5s (if you could so such a thing).

 

[cyclebytrain]

I think I need to chime in in this thread, because I can claim some minor knowledge about how GPS systems work.

The principle behind GPS is that each GPS satellite broadcasts the time and it's position (that's a slight over simplification). If you have the signal from four satellites, you can determine your position and the time based on how long it has taken a signal to travel from where the satellite is to where you are (remember your basic maths, there are four unknowns (x,y,z and time) so you need four simultaneous equations (i.e. satellites)). So then you know your position in 3d space and time.

That's the theory. Unfortunately the implementation is not quite(!) so simple. There are a couple of key issues.

Firstly, you may only be able to get a signal from three satellites. Four unknowns, three equations. That doesn't work. However, since the earth is roughly circular and the GPS receiver knows the typical radius (actually most modern receivers know a good bit more than that) if it can't get four satellites it will assume that you are on the average surface and give you your position in 2d as Lat/Lon on the basis that this is quite likely and a lot more useful than saying "sorry, no position fix available". This is where the rumours about GPS being 2d come from.

Secondly, you can't solve the simultaneous equations analytically, you have to do it arithmetically (if you don't understand what this means, just take my word for it that this degrades the accuracy because the theory says that to get a perfectly accurate fix would take an infinite amount of time).

Finally, if you've followed this far speed and heading indications from most GPS units aren't the result of the difference between two position fixes, they are calculated in yet another way -and I'm not happy trying to explain how that works!

(Also, I haven't mentioned augmentation signals or DGPS here but I think that would complicate things unnecessarily)


So in summary, GPS as a system is very accurate when working perfectly and degrades very gracefully, but many implementations don't tell you when the accuracy is degraded which can confuse.

And since I'm quite drunk whilst writing this, if anyone has managed to follow it, I'm very impressed

 

[TGV]

And since I'm quite drunk whilst writing this, if anyone has managed to follow it, I'm very impressed

I think you've deserved another drink! Interesting summary - tell us more when you're sober!

 

[cyclebytrain]

What do you want to know? There's about another half hour before I arrive (very appropriately, I'm travelling along the WCML right now

 

[TGV]

My Holux data logger aqcuires signal much faster than a Tom Tom sat nav unit. It also keeps it better in built up areas - I am led to conclude this is due to the differences in chip sets (The Holux uses a SiRFStarIII chip - I don't know what the Tom Tom has). Or is it similar to the theory that simpler mobile phones can use higher gain on the antenna signal because the antenna is larger and there's less likely interference with other chips on the same board?

Jeez - I'm sober and I can't write that question any better... sorry! I do trains for a living you see - not electronics!

 

[cyclebytrain]

How you filter the signal can make a hell of a lot of difference. That side of things is pretty much black magic to me, but for holding everything else constant, different filtering can make massive differences.

Different chips make a difference too, but all of chips of a given generation are fairly similar. Obviously if you compare a generation 1 against a generation 2, you would expect the generation 2 to do better.

In relation to built up areas, the most common problem is reflected signals from buildings -so instead of travelling directly from the satellite to your receiver the signal bounces around between several buildings and therefore arrives late, screwing up the fix. If you can track 16 or 32 satellites, you can get a better handle on what is going on than if you can only track 4 (this is a chipset function).

However, like everything, it's very easy to screw it up with bad design!

P.S. I do UAv autopilots for a living, so this sort of thing is quite important for me to know -at least in broad terms

 

[Pumbaa]

Don't Pendolinos have a speed hold function?

They do I think - but its not very useful. I think it holds current power levels relative to a computerised reading of wheel resistance at the time of the application, so as soon as the gradient changes it will either freewheel out of control or slow up.

I think thats how it works, but absolutely sure. As I said earlier, if Respite glances over this thread, he should be able to give a definite answer!

 

[western Champion]

Nope - the speedo will start having a hissy fit and set off alarms at 126. Driver then has 7 seconds to reduce speed before E Brake application. They can't turn off the safety either - it radios through to WCT control at Edge Hill/Wembley that the action has been taken. Whoever is watching will then confirm they had permission to, ie shunting over failed grids, and if not they can remote monitor the train while contacting the signal box to ask the driver why the hell he's done it.

Of the top of my head from Rugby to London, coming away from Rugby is 125 (all speeds top EPS for 390s) to the tunnels, where it's 115/110, then you have 125 again until away from the motorway, down to 110, then 115 through the last curves, then 125 all the way down to Bletchley, 110 across Bletchley South (will be 125 after upgrades finished), 125 to Leighton, 115 through the tunnels, 125 through Berko (impressive to say the least), 125 all the way to Bushey Viaduct, 115 across that, then 125 to Harrow, then 115 to Wembley Central, then down to 110, 100 and into Euston approaches.

They will run at linespeed, unless a service in front is schedule to make a stop, the drivers will adjust accordingly to minimise braking.

Pumbaa where do you get your miss information from ?

1st :- Tass will not give a warning of over speed until 3.5 mph over maximum speed, therefore if line speed is 125 then that's 128.5

2nd :- A mod on Pendo's means that power is ramped down over 125 mph to avoid the situation above.

3rd :- The train does not radio to anybody ! any intervention by Tass and for that matter any thing else regarding the running of the train is simply recorded on OTMR and is available to maintenance / Driver Managers through a download. The train does report serious faults directly to the maintenance engineer in control but this certainly does NOT include any speeding incidents.

The train can be dialled into remotely by the engineer in control should he wish to monitor a specific train.

4th :- Now for your EPS line speeds for Pendos to Euston...

It is 125 through Rugby and through to Kilsby, 110 through the tunnel then back to 125 until Weedon. 120 round Weedon then 125 all the way to Watford tunnel. 110 through the tunnel and station then back to 125 just before Bushey. 125 until roughly opposite Wembley Depot where it drops to 110. Then 105 after Kensal Green tunnel. 80 at Queens Park. 55 through Primrose Hill tunnel. 50 out the tunnel. 40 at Park Street and 25 from the last signal and through out the station area (Assumes using lines A, B, C or D).

 

[Pumbaa]

1st :- Tass will not give a warning of over speed until 3.5 mph over maximum speed, therefore if line speed is 125 then that's 128.5

2nd :- A mod on Pendo's means that power is ramped down over 125 mph to avoid the situation above.

3rd :- The train does not radio to anybody ! any intervention by Tass and for that matter any thing else regarding the running of the train is simply recorded on OTMR and is available to maintenance / Driver Managers through a download. The train does report serious faults directly to the maintenance engineer in control but this certainly does NOT include any speeding incidents.

The train can be dialled into remotely by the engineer in control should he wish to monitor a specific train.

We were told that all the above information was available to the folks watching the systems at Edge Hill and Wembley on demand, and that overspeeding was one of them, including that TASS had a tolerance of only 1mph. Certainly from where I was standing, one service that was dialled into gave a route profile of speed since the train had started its journey.

4th :- Now for your EPS line speeds for Pendos to Euston...

It is 125 through Rugby and through to Kilsby, 110 through the tunnel then back to 125 until Weedon. 120 round Weedon then 125 all the way to Watford tunnel. 110 through the tunnel and station then back to 125 just before Bushey. 125 until roughly opposite Wembley Depot where it drops to 110. Then 105 after Kensal Green tunnel. 80 at Queens Park. 55 through Primrose Hill tunnel. 50 out the tunnel. 40 at Park Street and 25 from the last signal and through out the station area (Assumes using lines A, B, C or D).

Last sectional I had is for before the south of MK was officially finished, I was going off that and had done for the last few years. Ta for the update.

 

[western Champion]

We were told that all the above information was available to the folks watching the systems at Edge Hill and Wembley on demand, and that overspeeding was one of them, including that TASS had a tolerance of only 1mph. Certainly from where I was standing, one service that was dialled into gave a route profile of speed since the train had started its journey.



Last sectional I had is for before the south of MK was officially finished, I was going off that and had done for the last few years. Ta for the update.

Pumbaa, it sound like you need a cab ride to Euston and maybe then you'll forget the rubbish you've been told by Alstom. (No I'm not offering, the're awkward enough to arrange even for relatives.)

 

[Pumbaa]

Pumbaa, it sound like you need a cab ride to Euston and maybe then you'll forget the rubbish you've been told by Alstom.

You offering?

But seriously, I think I need to apply a disclaimer to all my knowledge about the 390s from here on! There's an event at Edge Hill at the end of April, so I may interrogate them then.

To kind of drag the thread back on topic, I'm guessing you'd have done a non-EPS run down the TV. How much longer does it take to do Crewe - London non-EPS? A noticeable difference? I'd hazard a guess at around 9/10 mins extra.

 

[western Champion]

You offering?

But seriously, I think I need to apply a disclaimer to all my knowledge about the 390s from here on! There's an event at Edge Hill at the end of April, so I may interrogate them then.

To kind of drag the thread back on topic, I'm guessing you'd have done a non-EPS run down the TV. How much longer does it take to do Crewe - London non-EPS? A noticeable difference? I'd hazard a guess at around 9/10 mins extra.

Yeah about that, enough to come close to failing PPM.