Acceleration/breaking distances for sprinter units

[Rhydgaled]

I'm trying to get an idea of how long a section needs to be for it be to be worth upgrading linespeeds. Therefore I would like to know the acceleration/breaking distances for sprinter units (specificly 150s, 153s/155s, 156s and 158s) so that I can measure sections using Google earth. For each of these unit classes I would like to know:

• The distance required to accelerate from 0 to 60mph
• The distance required to accelerate from 60mph to 75mph (therefore giving me the distance from 0 to 75 if I add them up)
• The distance required to accelerate from 75mph to 90mph (158 only obviously)
• The distance required to break from 90mph back down to 75, and from there to 60 and there to 0.

I would also be interested to know the minimum radius of curves required to reach these speeds.

 

Google hasn't been my friend here, so please help, thanks in advance if you can.

[96701]

Two words - low adhesion.

 

Joking apart, you are requesting the sort of information that would only be available to Network Rail planners, so you could be really struggling to manage such a large amount of data, if anybody could find it.

[Guest stuartp]

Braking on the level on a dry rail - within the curves on pages 9-12 of this document, and its successors. Everything else - as Mickey suggests it depends on gradient, railhead conditions, curvature, loading, when the engine was last overhauled, temperature, headwinds, driving technique etc etc.

 

I doubt Google or anything else will be your friend on this for 15x units as they predated widespread use of computer modelling which is how most of these things are calculated. I had to establish the braking distance in ideal conditions for a 156 as part of the investigation into RRNE's fatal collision at Ais Gill in 1995. It took the boffins at Derby some time to come up with a braking curve, and when it arrived it was hand drawn on graph paper. I've still got it, it comes in useful for inquests sometimes, but I can't publish it (sorry).

 

If you do find an online source, I'd love to know ! There must be some figures for timetable planning somewhere but I would guess they would be generic, there are too many variables involved for them to be anything else.

[stadman]

There are certainly a multitude of factors, no doubt all mentioned above.

Even differing driving techniques of various drivers, experience, etc all play a factor.

From a modelling point probably won't make any difference.

Curves would probably extend the distances.

Kevin Staddon

[Edwin_m]

It is possible to do this for acceleration by measuring time from start to each quarter milepost passed using a stop watch, when starting from a station on reasonably level track and free from speed restrictions. Stop recording when you hear the driver shut off power! You will need the milepost distance of the starting station which is shown on Quail maps. If you do several runs and average them, the results can be plotted on a speed-distance graph and if you fit a curve to this you can read off the distance to accelerate from one speed to another. I've done this myself but as it's for work I can't release the results I'm afraid.

 

Timetabled running times are based on a deceleration of about 6%g (about 0.6m/s2) for 158 and similar units that can actually achieve 9%g in service. This is pretty much constant across the speed range so stopping distances (in metres) can be worked out as the square of the speed (in metres per second) divided by twice the deceleration rate (in m/s2).

[great central]

There must be theoretical values for all this, but in practice not even two units of the same type will perform the same.

There are good ones and bad ones, permanently so, in all types.

Most of our 153s struggle to keep time on most jobs, so I would say that the theoretical timings are too ambitious. The 153s have the worst power/weight ratio of any of the sprinters, also being a single car affects their aerodynamics as well, they work much better even as a pair of 153s. There is one though that confounds the odds and actually gains time!

I had a 158 recently which at one point should have been doing around 75mph at a particular point and it was doing 45, downhill at that! Although I believe it may have had a serious engine failure earlier this week.

Braking depends on the driver, some break early and light, a few it's step 3 everywhere.

[Edwin_m]

The 153s always seem very sluggish in getting away from stations and you often hear what sounds like brake squeal as they move off. I suspect (but I don't know) that when they were made into single units they had to duplicate some parts of the brake system for safety when running alone, and they didn't bother to upgrade other parts so they are now a little short of air.

[Rhydgaled]

Well, thanks for the replies everyone. There's two things I'm trying to figure out, which is why I'm asking these questions. These figures only need to be suitable for setting up a timetable, I expect a safe figure is used that allows for some variation in driving styles etc. so I don't need to be all that specific. I expect gradient is the variation most likely to be an issue here, so roughly how much difference would it make?

• Thing 1 - There is a service running non-stop between point A and point C with a Class 150 unit, but there are 90mph linespeeds on this section. I'm wondering how much time using a 158 instead would save, and whether the 158 could make an additonal stop at point B without making the journey from A to C longer than the 150 can manage without the stop. If I knew the figures I expect I could measure the distances with Google Earth and work it out roughly, although knowing excatly where the 90mph linespeeds end would be handy too.
• Thing 2 - I'm wondering what time saving would be achived if a different section of line was upgraded to a 90mph linespeed, and after acceleration and breaking what distance of the upgraded track would actually be run over at 90mph.

I'm therefore looking for a fairly rough figure, say 2,000 meters (from a glance at supplied linked PDF this looks a safe bet for breaking distance from 90mph), for these, hope you can help.

 

 

[dmustu]

The 153s always seem very sluggish in getting away from stations and you often hear what sounds like brake squeal as they move off. I suspect (but I don't know) that when they were made into single units they had to duplicate some parts of the brake system for safety when running alone, and they didn't bother to upgrade other parts so they are now a little short of air.

 

When I had the pleasure of signing 153's many years ago, they always struggled to depart stations, this seemed to be largley due to the brakes on the No. 2 bogie being much slower to release than the ones on the No. 1 bogie, which is why you hear the brake squeal when they're trying to depart. This only seemed to happen when running as a single car, when coupled to other units, the slow brake release on the No. 2 bogie didn't happen! Sprinters can be quite strange at times.

[Edwin_m]

That I think would be consistent with the on-board equipment using more air than the vehicle can produce. When coupled to something else the air supply would be shared via the train pipe.

[great central]

Well, thanks for the replies everyone. There's two things I'm trying to figure out, which is why I'm asking these questions. These figures only need to be suitable for setting up a timetable, I expect a safe figure is used that allows for some variation in driving styles etc. so I don't need to be all that specific. I expect gradient is the variation most likely to be an issue here, so roughly how much difference would it make?

• Thing 1 - There is a service running non-stop between point A and point C with a Class 150 unit, but there are 90mph linespeeds on this section. I'm wondering how much time using a 158 instead would save, and whether the 158 could make an additonal stop at point B without making the journey from A to C longer than the 150 can manage without the stop. If I knew the figures I expect I could measure the distances with Google Earth and work it out roughly, although knowing excatly where the 90mph linespeeds end would be handy too.
• Thing 2 - I'm wondering what time saving would be achived if a different section of line was upgraded to a 90mph linespeed, and after acceleration and breaking what distance of the upgraded track would actually be run over at 90mph.

I'm therefore looking for a fairly rough figure, say 2,000 meters (from a glance at supplied linked PDF this looks a safe bet for breaking distance from 90mph), for these, hope you can help.

 

I'm not sure there would be a huge difference in practice, a 150 seems quicker off the mark than a 158, but of course it has a lower top speed.

I don't sign 150s but a 156 put on a long distance 158 job will pretty much keep time, whereas a 158 put on a stop start job sometimes struggles a bit due to it's slower acceleration, although the braking should be superior.

[Bomag]

Something which has not been mentioned is curvature. Having spent several weeks in 1989 trying to get the Breckland bends on the Ely to Norwich line to work at 90mph you only need one short transition or a tricky reverse to negate 5+ miles of improvements.

[Lady_Ava_Hay]

I'm trying to get an idea of how long a section needs to be for it be to be worth upgrading linespeeds. Therefore I would like to know the acceleration/breaking distances for sprinter units (specificly 150s, 153s/155s, 156s and 158s) so that I can measure sections using Google earth. For each of these unit classes I would like to know:

• The distance required to accelerate from 0 to 60mph
• The distance required to accelerate from 60mph to 75mph (therefore giving me the distance from 0 to 75 if I add them up)
• The distance required to accelerate from 75mph to 90mph (158 only obviously)
• The distance required to break from 90mph back down to 75, and from there to 60 and there to 0.

I would also be interested to know the minimum radius of curves required to reach these speeds.

 

Google hasn't been my friend here, so please help, thanks in advance if you can.

 

Even if you had these statistics, it wouldn't mean anything. As an ex bus driver I can assure you that there is no computer that could be afforded that can cope with the vagaries of the organic things that drive, use and generally mess up the best laid plans (timetables) let alone the other variables that govern a trains performance in service.

 

Remember also tha ta lot of these lines were all laid out over a hundred years ago when it was pretty certain that 30 or 40 mph would be the most that would be possible.

 

I have seen the results of a cost conscious management attempting to squeeze four buses work onto three buses and the resulting mayhem. It is poring over the sort of statistics you seek that causes this mayhem because some bright spark takes raw data like this and attempts to build a working timetable around it.

[Edwin_m]

I agree there are lots of issues that affect line speed improvements including track condition curvature, vertical curvature, state of structures, braking distance to signals, strike-in for level crossings, ground conditions and many more. Some lines are pretty easy to upgrade, others are very difficult, and it's not always easy to tell which without a lot of research.

 

Also if you ask Network Rail why a particular piece of track has a particular speed restriction, then they probably won't tell you unless you pay, and even if they are willing they often don't know because the person that originally decided it has retired long ago and didn't leave any records.

[Edwin_m]

150 and 155/153 were built for short distance, start/stop journeys so they do accelerate (or are meant to) quite well ..156/158 were built for longer trips with less stops - On local Inter-Urban services a 158 loses time on a Pacer diagram - though that is more to do with the station stop times a 158 needs than the perfromance of the unit... Plug Doors dont seem to like opening and closing all the time.

 

The point-to-point timings of classes 150 and 156 are identical. The 156 needs more time at busier stations because of the door layout, but not as much as the 158.

[great central]

150 and 155/153 were built for short distance, start/stop journeys so they do accelerate (or are meant to) quite well ..156/158 were built for longer trips with less stops - On local Inter-Urban services a 158 loses time on a Pacer diagram - though that is more to do with the station stop times a 158 needs than the perfromance of the unit... Plug Doors dont seem to like opening and closing all the time.

 

If they've been set up on the 'light' side, they won't even close at some stations if you're on a cant, reaaly screws up your dwell times! A tad annoying when we used to do five (yes 5) Derby-Matlocks in an evening.

Then there are others that close with such a bang you think they'll break the operating arms.

[big jim]

I don't sign 150s but a 156 put on a long distance 158 job will pretty much keep time, whereas a 158 put on a stop start job sometimes struggles a bit due to it's slower acceleration, although the braking should be superior.

 

i always found 156's to be a better unit than 158's from a drivers point of view, clasp brakes etc but i do have to say that 165's are pretty damn good accellerating and braking compared to a 158 considering they are pretty much the same drivetrain

 

regards the doors you can guarentee the sticky door is the back one, unfortunatly we dont have guards as we are doo

[The Stationmaster]

Rules Of The Plan quotes 5 different acceptable methods for calculating sectional running times plus at least two variants in the way in which they are then used. The simplistic method was always to use the same start and stop allowances irrespective of train type and then simply calculate the point to point running time and add the allowances - and that would almost invariably be within 1.5 minutes of the Derby computer run calculation for most sectional times.

 

It was the method I normally used for quick assessment jobs and it was usually accurate enough for investment decisions at 20% tolerance (in fact on those occasions when my calculations were tested againt the then (early 1990s)available 'easy use' computer programmes I was usually within 5% or less of their output - and that would usually vanish in the rounding in any case

 

Depending on what you want to use it for there really isn't much point in looking for the sort of finesse in initial calculations which you seem to want. Trains are timed rounded to the nearest half minute, and it's normally rounded up to that half minute. A mile travelled at 90mph is is 8 seconds quicker than a mile travelled at 75mph and 20 seconds quicker than one travelled at 60mph so unless you are looking at large increases (say, 60 to 90) you might have to cover a lot of miles before you find a minute of saving.

 

So - having in the past got the tee-shirt on such schemes as the Ebbw Valley - my advice is always to do the quick & dirty simple maths before even wondering if it is worth going in for anything sophisticated. And go out and buy a few recent secondhand working timetables and work out the sectional running times from them. If you want to get anything more detailed go out with a stopwatch (which is in fact one of the five permissible methods).

 

Incidentally you will not (or rather should not) be able to find sectional running times on the internet as they are confidential between each operator and NR and are therefore not included in the publicly available ROTP files.

[Rhydgaled]

Rules Of The Plan quotes 5 different acceptable methods for calculating sectional running times plus at least two variants in the way in which they are then used. The simplistic method was always to use the same start and stop allowances irrespective of train type and then simply calculate the point to point running time and add the allowances - and that would almost invariably be within 1.5 minutes of the Derby computer run calculation for most sectional times.

 

It was the method I normally used for quick assessment jobs and it was usually accurate enough for investment decisions at 20% tolerance (in fact on those occasions when my calculations were tested againt the then (early 1990s)available 'easy use' computer programmes I was usually within 5% or less of their output - and that would usually vanish in the rounding in any case

 

Thanks, a 'simplistic method', especially if any difference would vanish in rounding, is probablly all I need, and using Google Earth my measurements are probablly not going to be perfectly accurate anyway. After what everyone else has said I'm a little supprised that the same stop and start allowances apply to the different train types but I'd go with that if I knew what the allowances were (is 2,000 meters about right?). Could you provide the standard stop/start allowances please? From what I've heard acceleration rate drops at higher speeds (a curve on a graph rather than a straight line) so maybe there's different allowances I would need to make for that?

 

P.S. There's also a thing 3, where a dismantled railway (the line from Carmarthen to Aberystwyth) is described as being tortuous and would be slower than the bus if re-opened. Looking at the line on Google Earth I don't agree, sure it's really twisty but I've only made a circle of 90mph radius to compare it with and from that I'm vaugely guessing the train would still be able to do 60mph minimum (except for when accelerating/decelerating). Maybe it has more to do with cant/superelevation/whatever it's called (and the distance required between curves in different directions to allow enough cant) than I expect.

[The Stationmaster]

I dont know the former line in question, but I think you might be over estimating the permitted speeds a fair bit. west of Plymouth the maximum line speed is only 70mph, and that allegedly a main line......

 

Ditto - I doubt if Carmarthen-Aberystwyth could be pushed above 60mph without a very large amnmount of extra money being spent!

 

I did some work a while back on a possible reopening of a long closed route where the promoters were looking at a 90mph linespeed for much of it. As some of it had been 60mph or a bit more in steam days a lot of the geometry of the formation in terms of curvature (horizontal and vertical) would be a reasonable starting point for higher speed. Perway costs had been estimated by a recognised contractor in the field - a company well used to relaying work on existing formation. But the highly experienced Perway engineer I was working with reckoned that notwithstanding the work they had done they were probably around £2million out (too low) on their cost estimate because of not taking into account the extra formation work needed for such a big step change in speed.

 

Start and stop allowances used to be 1 minute to start and half a minute to stop. With modern dmus the start allowance can probably be reduced but that depends on the speed you are looking to attain.

[Etched Pixels]

P.S. There's also a thing 3, where a dismantled railway (the line from Carmarthen to Aberystwyth) is described as being tortuous and would be slower than the bus if re-opened. Looking at the line on Google Earth I don't agree, sure it's really twisty but I've only made a circle of 90mph radius to compare it with and from that I'm vaugely guessing the train would still be able to do 60mph minimum (except for when accelerating/decelerating). Maybe it has more to do with cant/superelevation/whatever it's called (and the distance required between curves in different directions to allow enough cant) than I expect.

 

Lots of things play into this - the bridge strengths, the groundworks in general, visibility, crossings - nothing like a good level crossing to ruin it. and gradients. If the description was written in the days of steam or gen 1 DMU stock then they really didn't do hills the same way as modern stock. Not that it matters for that route - the politicians and civil servants all live in Cardiff and the Crachach amongst them who live up Aber way wouldn't want to go the long way around. More chance (still nil) of Merthyr-Brecon- Builth route up.

[Rhydgaled]

I doubt if Carmarthen-Aberystwyth could be pushed above 60mph without a very large ammount of extra money being spent!

So you would agree with my vauge guess guess that the train would still be able to do 60mph on the orriginal curvature? As I said, even with the train doing 60 I doubt a bus would be faster. Also if west of Plymouth is 70mph then I would think Carmarthen - Aberystwyth should be able to manage 60 as the curvature doesn't look that much worse to me.

Start and stop allowances used to be 1 minute to start and half a minute to stop. With modern dmus the start allowance can probably be reduced but that depends on the speed you are looking to attain.

Thanks, so if the distance between points A & C is such that doing 90 versus 75 would save at least 2mins 30secs the train can stop at B and still reach C in the same length of time?

 

More chance (still nil) of Merthyr-Brecon- Builth route up.

As far as a Cardiff - Bangor route is concerned that is the one I would support I think. I'm looking at the line north from Carmarthen to plug one of the gaping holes in the rail network, not as a through link from Swansea/Cardiff to anywhere north of Aberystwyth (because you'd have to go to Dovey Junction and reverse to go north).

[stadman]

this seemed to be largley due to the brakes on the No. 2 bogie being much slower to release than the ones on the No. 1 bogie, which is why you hear the brake squeal when they're trying to depart.

 

I think there is a choke in the exhsut from the air cylinder on No 2 but not all

[Kris]

As I said, even with the train doing 60 I doubt a bus would be faster. Also if west of Plymouth is 70mph then I would think Carmarthen - Aberystwyth should be able to manage 60 as the curvature doesn't look that much worse to me.

 

 

That is the maximum line speed west of Plymouth. From memory most of the line has a lower line speed than this.

 

 

[Etched Pixels]

[/i]So you would agree with my vauge guess guess that the train would still be able to do 60mph on the orriginal curvature? As I said, even with the train doing 60 I doubt a bus would be faster. Also if west of Plymouth is 70mph then I would think Carmarthen - Aberystwyth should be able to manage 60 as the curvature doesn't look that much worse to me.

Thanks, so if the distance between points A & C is such that doing 90 versus 75 would save at least 2mins 30secs the train can stop at B and still reach C in the same length of time?

 

 

As far as a Cardiff - Bangor route is concerned that is the one I would support I think. I'm looking at the line north from Carmarthen to plug one of the gaping holes in the rail network, not as a through link from Swansea/Cardiff to anywhere north of Aberystwyth (because you'd have to go to Dovey Junction and reverse to go north).

 

Bingo - which is one reason it would never fly. It links two tiny centres of population most of whom don't wish to travel that way and have a perfectly good bus service, while the Cardiff route links the Crachach with their nice homes by the sea and provides a missing link through smaller but more relevant centres of population, plus the odd traveller from the west can just change at Builth Road as well as head North of Aber without problems.

 

And with a spur at Builth you can even build one half only.

 

Alan