5 ms·

Rail systems shine when they can concentrate steering an power in more efficient dedicated locomotives, with as many "dumb cars" as possible "automatically" fol

by jarfil 8y ago

Rail systems shine when they can concentrate steering an power in more efficient dedicated locomotives, with as many "dumb cars" as possible "automatically" following them (thanks to the rails). But in order to achieve higher granularity and better schedules, cars would have to become more autonomous, which means duplicate steering systems and lower efficiencies... unless there were no efficiency benefits in having a dedicated locomotive, in which case it would make no sense to join cars together in the first place.

greglindahl 8y ago
Dedicated locomotive? That's true for things like diesel freight trains, but most high speed electric trains have motors in every car because electric motors scale down just fine.
- war1025 8y ago
  My understanding is that freight trains use electric motors as well. The diesel engine acts as an electric generator rather than being connected directly to the drivetrain.
  - cup-of-tea 8y ago
    No engines have an internal combustion engine connected directly to the wheels. You can't get anywhere near enough torque. Steam engines have incredible torque. What you're describing is a diesel-electric and is essentially synonymous with saying diesel engine on the railway. There are also electro-diesels which can shut off their diesel engine and take electricity directly from an overhead line or third rail by raising a pantograph or lowering a boot. This used to happen at Faringdon in London (maybe still does).
    - tunareter 8y ago
      You're completely wrong. Most diesel locomotives are in fact diesel electrics. I.e. diesel engine, generator, electric motors. Most of those cannot use external power sources (although a few can, e.g. class 73 in the UK). Certainly in the UK: the most common locomotives such as class 66, 60, 58, 67, 47 - they're all diesel electric. In the US, same story: for passengers the GE Genesis is pretty big, things like SD90MAC and AC6000CW are big for freight.
      - cup-of-tea 8y ago
        I think you misread my comment.
    - pmyteh 8y ago
      There are non-trivial numbers of diesel-mechanical (IC to wheels via a gearbox) and diesel-hydraulic (IC to wheels via a fluid coupling) trains out there. The British class 172 Turbostar is an example of the former, most other class 1xx DMUs the latter. Diesel electric transmission does happen on smaller multiple units sometimes, but really shines on larger and faster trains, or on electro-diesels (where you need the electric final drive anyway).
    - isostatic 8y ago
      Doubt Farringdon switched from diesel to overhead - overhead to third rail. Some trains have to stop to raise the pantograph, some do it on the fly (I think the 395s can switch 3rd rail to ohel at 60mph when coming on/off hs1) Some trains are hybrid - will use electricity while under wires, and switch to diesel when there's no wires, the new class 800 in the UK as an example.
      - cup-of-tea 8y ago
        It was diesel to overhead. It was the Thameslink train and I think it used diesel south of London (to Brighton).
        isostatic 8y ago
        When the snow hill tunnel re-opened in 1988, and trains started from Farringdon to Blackfriars, they were operated by class 319s, which were dual voltage from the very start. While I'm sure some diesel engineering trains have been through the tunnels, and perhaps some diesel goods trains in the 60s before the closure, I'm not aware of any diesel passenger trains through them (as there were no passenger trains since 1916) Some 319s are being converted to partial diesel and becoming class 769s, but not on this route.
        cup-of-tea 8y ago
        Oh it could have been switching from overhead to third rail... I never actually went on the train to Brighton, I just remember the pantograph coming down.
        isostatic 8y ago
        Still does it now, there's a similar switchover north of Shepherds Bush. The Southern 350s used to stop when I got that train, I think the overground trains can raise/lower on the fly. I assume there's a similar changeover in East London. Before 2009 and HS1 to St Pancras, Eurostar also switched from overhead to third rail, on the fly I think, somewhere near Ashford.
- cup-of-tea 8y ago
  Most, if not all, high speed trains operate as "train sets". They don't split arbitrarily. Some like ICE use smaller sets that can join. Others, like Eurostar, are fixed. Some inner-city rail in Europe is like you describe but not anything high speed (>~100mph) AFAIK.
  - tialaramex 8y ago
    The technical term you're looking for is "multiple unit", and you're correct that in a multiple unit it is not possible to arbitrarily couple together arbitrary carriages, re-arranging the multiple unit is possible only at dedicated maintenance facilities and may require a complete refit. However everything else you've claimed is wrong. The designs you're talking about DO have motors under many (or in some cases all) passenger coaches driving the wheels, rather than a dedicated "locomotive" so they support your parent's point, not yours. The original Eurostar (class 373) trains are confusing because they're built as multiple units but the lead and trailing cars basically just provide traction, so the result looks a lot like a "conventional" locomotive plus carriages. But modern Eurostar (class 374) looks exactly like any other multiple unit and has motors distributed across the whole train. Britain does operate a bunch of locomotive pulled high speed (125mph) services, but it also owns a bunch of 125mph multiple units. Even the Desiro 444 and 450 trains could do 125mph if not for the fact they're configured exclusively for third rail power limited to 100mph. The reason none of those trains exceeds 125mph is purely down to legal/ safety considerations. Britain uses coloured light signals with route control, as speeds increase drivers struggle to correctly interpret and act on a light signal by the side of the track. HS-1 (Eurostar) and many European high speed services have in-cab signals, so the driver doesn't need to try to observe fixed coloured light signals at the side of the track, the indications are inside the cab with them. As well as the reasons given earlier about improved performance from distributing the traction power across the train, distributing the weight also improves crash performance. Heavy locomotives will tend to crush a lightweight passenger car, if we make all the cars of more similar weight this problem goes away.
    - cup-of-tea 8y ago
      > However everything else you've claimed is wrong. Eh? I didn't say anything at all about where the motors were. You're the second person in this thread to imagine me saying something wrong and call me out on it.
7952 8y ago
Modern passenger trains have motors spread throughout the entire train. It allows them to accelerate better than is possible with a dedicated power car. This is because multiple wheels have more contact with the track. Modern diesel trains have multiple smaller generators spread throughout the train rather than dedicated power cars. Both these approaches give better modularity as the power availabile scales with the length of a train. The efficiency gain in splitting trains is mostly related to reducing the number of drivers needed. It also reduces the demand on track and platforms that may be congested. Both these things could be solved through better automation. Have the train driven by a computer and automate signalling to allow trains to run closer together.
tialaramex 8y ago
I'm loving how nobody has called out the fact that this comment pretends trains have "steering systems" and need to "concentrate steering" in locomotives.
- operationer 8y ago
  https://en.wikipedia.org/wiki/Point_machine https://en.wikipedia.org/wiki/Point_machine It would be kind of tedious to go into great detail. Feels like nerd sniping.
- teh_klev 8y ago
  I hate to "well actually"...but some loco's do actually have steerable bogies (or trucks). The class 66 is an example of such a loco which permits it to go pretty much anywhere on the UK rail network where the track would previously only allow lighter and less powerful engines. https://www.youtube.com/watch?v=2OGRwD-00b8 https://www.youtube.com/watch?v=2OGRwD-00b8 https://patents.google.com/patent/US20030230213 https://patents.google.com/patent/US20030230213 Not sure if this is what jarfil meant by "steering".
honestoHeminway 8y ago
Just dont take the engine and steering along then- the car is propelled and steered out of the station by the rail, brought up to speed, and attached in a gap behind the engine.

by jarfil 8y ago

greglindahl 8y ago

Dedicated locomotive? That's true for things like diesel freight trains, but most high speed electric trains have motors in every car because electric motors scale down just fine.

war1025 8y ago
My understanding is that freight trains use electric motors as well. The diesel engine acts as an electric generator rather than being connected directly to the drivetrain.
- cup-of-tea 8y ago
  No engines have an internal combustion engine connected directly to the wheels. You can't get anywhere near enough torque. Steam engines have incredible torque. What you're describing is a diesel-electric and is essentially synonymous with saying diesel engine on the railway. There are also electro-diesels which can shut off their diesel engine and take electricity directly from an overhead line or third rail by raising a pantograph or lowering a boot. This used to happen at Faringdon in London (maybe still does).
  - tunareter 8y ago
    You're completely wrong. Most diesel locomotives are in fact diesel electrics. I.e. diesel engine, generator, electric motors. Most of those cannot use external power sources (although a few can, e.g. class 73 in the UK). Certainly in the UK: the most common locomotives such as class 66, 60, 58, 67, 47 - they're all diesel electric. In the US, same story: for passengers the GE Genesis is pretty big, things like SD90MAC and AC6000CW are big for freight.
    - cup-of-tea 8y ago
      I think you misread my comment.
  - pmyteh 8y ago
    There are non-trivial numbers of diesel-mechanical (IC to wheels via a gearbox) and diesel-hydraulic (IC to wheels via a fluid coupling) trains out there. The British class 172 Turbostar is an example of the former, most other class 1xx DMUs the latter. Diesel electric transmission does happen on smaller multiple units sometimes, but really shines on larger and faster trains, or on electro-diesels (where you need the electric final drive anyway).
  - isostatic 8y ago
    Doubt Farringdon switched from diesel to overhead - overhead to third rail. Some trains have to stop to raise the pantograph, some do it on the fly (I think the 395s can switch 3rd rail to ohel at 60mph when coming on/off hs1) Some trains are hybrid - will use electricity while under wires, and switch to diesel when there's no wires, the new class 800 in the UK as an example.
    - cup-of-tea 8y ago
      It was diesel to overhead. It was the Thameslink train and I think it used diesel south of London (to Brighton).
      - isostatic 8y ago
        When the snow hill tunnel re-opened in 1988, and trains started from Farringdon to Blackfriars, they were operated by class 319s, which were dual voltage from the very start. While I'm sure some diesel engineering trains have been through the tunnels, and perhaps some diesel goods trains in the 60s before the closure, I'm not aware of any diesel passenger trains through them (as there were no passenger trains since 1916) Some 319s are being converted to partial diesel and becoming class 769s, but not on this route.
        cup-of-tea 8y ago
        Oh it could have been switching from overhead to third rail... I never actually went on the train to Brighton, I just remember the pantograph coming down.
        isostatic 8y ago
        Still does it now, there's a similar switchover north of Shepherds Bush. The Southern 350s used to stop when I got that train, I think the overground trains can raise/lower on the fly. I assume there's a similar changeover in East London. Before 2009 and HS1 to St Pancras, Eurostar also switched from overhead to third rail, on the fly I think, somewhere near Ashford.
cup-of-tea 8y ago
Most, if not all, high speed trains operate as "train sets". They don't split arbitrarily. Some like ICE use smaller sets that can join. Others, like Eurostar, are fixed. Some inner-city rail in Europe is like you describe but not anything high speed (>~100mph) AFAIK.
- tialaramex 8y ago
  The technical term you're looking for is "multiple unit", and you're correct that in a multiple unit it is not possible to arbitrarily couple together arbitrary carriages, re-arranging the multiple unit is possible only at dedicated maintenance facilities and may require a complete refit. However everything else you've claimed is wrong. The designs you're talking about DO have motors under many (or in some cases all) passenger coaches driving the wheels, rather than a dedicated "locomotive" so they support your parent's point, not yours. The original Eurostar (class 373) trains are confusing because they're built as multiple units but the lead and trailing cars basically just provide traction, so the result looks a lot like a "conventional" locomotive plus carriages. But modern Eurostar (class 374) looks exactly like any other multiple unit and has motors distributed across the whole train. Britain does operate a bunch of locomotive pulled high speed (125mph) services, but it also owns a bunch of 125mph multiple units. Even the Desiro 444 and 450 trains could do 125mph if not for the fact they're configured exclusively for third rail power limited to 100mph. The reason none of those trains exceeds 125mph is purely down to legal/ safety considerations. Britain uses coloured light signals with route control, as speeds increase drivers struggle to correctly interpret and act on a light signal by the side of the track. HS-1 (Eurostar) and many European high speed services have in-cab signals, so the driver doesn't need to try to observe fixed coloured light signals at the side of the track, the indications are inside the cab with them. As well as the reasons given earlier about improved performance from distributing the traction power across the train, distributing the weight also improves crash performance. Heavy locomotives will tend to crush a lightweight passenger car, if we make all the cars of more similar weight this problem goes away.
  - cup-of-tea 8y ago
    > However everything else you've claimed is wrong. Eh? I didn't say anything at all about where the motors were. You're the second person in this thread to imagine me saying something wrong and call me out on it.

7952 8y ago

Modern passenger trains have motors spread throughout the entire train. It allows them to accelerate better than is possible with a dedicated power car. This is because multiple wheels have more contact with the track. Modern diesel trains have multiple smaller generators spread throughout the train rather than dedicated power cars. Both these approaches give better modularity as the power availabile scales with the length of a train. The efficiency gain in splitting trains is mostly related to reducing the number of drivers needed. It also reduces the demand on track and platforms that may be congested. Both these things could be solved through better automation. Have the train driven by a computer and automate signalling to allow trains to run closer together.

tialaramex 8y ago

I'm loving how nobody has called out the fact that this comment pretends trains have "steering systems" and need to "concentrate steering" in locomotives.

operationer 8y ago
https://en.wikipedia.org/wiki/Point_machine https://en.wikipedia.org/wiki/Point_machine It would be kind of tedious to go into great detail. Feels like nerd sniping.
teh_klev 8y ago
I hate to "well actually"...but some loco's do actually have steerable bogies (or trucks). The class 66 is an example of such a loco which permits it to go pretty much anywhere on the UK rail network where the track would previously only allow lighter and less powerful engines. https://www.youtube.com/watch?v=2OGRwD-00b8 https://www.youtube.com/watch?v=2OGRwD-00b8 https://patents.google.com/patent/US20030230213 https://patents.google.com/patent/US20030230213 Not sure if this is what jarfil meant by "steering".

honestoHeminway 8y ago

Just dont take the engine and steering along then- the car is propelled and steered out of the station by the rail, brought up to speed, and attached in a gap behind the engine.