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Third rails are even more expensive for freight railroads. * Double stack well cars sit very low. There are currently no third rail installations in the US tha

Third rails are even more expensive for freight railroads. * Double stack well cars sit very low. There are currently no third rail installations in the US that wouldn't get sideswiped by a well car. So their installation would basically mean forgoing half of freight revenue. * Third rails have to operate at lower voltages due to the fairly small clearance to the ground, and so they require more frequent substations than higher voltage overhead wires.

toomuchtodo 5y ago
Have any resources you’d recommend for learning more about the logistics of third rail power systems? Would you happen to know what the clearance is for double stack well cars? Edit: excellent resources, thanks all for replying.
- jcranmer 5y ago
  The general clearance envelope you're looking at is AAR Plate H: https://commons.wikimedia.org/wiki/File:Gabarit_AAR_Plate-H.png https://commons.wikimedia.org/wiki/File:Gabarit_AAR_Plate-H....
- jabl 5y ago
  Third rail systems typically work at 1500V, can't go very much higher than that due to risk from arcing. Most overhead lines use 25kV, allowing much more power to be transferred, over longer distances. Which is why third rail systems are usually only seen in metro lines and similar. I'd guess in urban environments sprinkling more substations around isn't such a huge issue, as access to the power grid is seldom an issue. Also metro trains need much less power than a high speed passenger train or a heavy freight train.
  - bobthepanda 5y ago
    with metros the additional consideration is tunneling. generally speaking, third rail allows for a smaller tunnel diameter than overhead systems. (third rail is located near the wider section of tunnel in the middle whereas overhead requires extending the height.)
    - bluGill 5y ago
      There are overhead rails you can use in tunnels. Nothing stops the high voltage arc issue (the whole advantage of overhead is high voltage), but without all the equipment to tension the cables you don't need as much room and the power will be one the middle of the tunnel. Anyone building new tunnel should allow the little extra room for overhead, but retrofitting may not be worth it.
- danhor 5y ago
  Regarding overhead wires for double stacked cars, India has a freight corridor with very high overhead wires: https://en.wikipedia.org/wiki/Dedicated_Freight_Corridor_Corporation_of_India https://en.wikipedia.org/wiki/Dedicated_Freight_Corridor_Cor... This would probably be the way to go if the US would introduce electrified rail routes. An overview of Third rail vs. Overhead Wire from a transit perspective, but it's similar with freight https://www.youtube.com/watch?v=LGI9XuHE3P0 https://www.youtube.com/watch?v=LGI9XuHE3P0 TLDR: Grade crossings are more complicated, if not impossible Smaller voltage since it's closer to the ground and the grounded rails. Thus higher current & more losses, needing more power stations. This is probably way worse for freight, since it weighs more and there are long gaps between civilization on the routes.
  - bobthepanda 5y ago
    This is also already present in the US: http://2.bp.blogspot.com/-1BbF3QiAd-0/Ui9YbpGk-8I/AAAAAAAACC4/Skzmp1iCK5Q/w1200-h630-p-k-no-nu/container+clear+elec+lines.jpg http://2.bp.blogspot.com/-1BbF3QiAd-0/Ui9YbpGk-8I/AAAAAAAACC...
  - pmyteh 5y ago
    Grade crossings are fine for passenger multiple units (have pickup shoes at both ends of the train and a gap either side of the crossing) but not great for locomotives. The other big problem (in addition to the ones you've outlined) is that having miles of live conductor at ground level isn't particularly safe - for track crew, trespassers, or wildlife. Britain has essentially stopped installing third rail for all these reasons. It's all 25kV overhead now.
    - iggldiggl 5y ago
      > Grade crossings are fine for passenger multiple units (have pickup shoes at both ends of the train and a gap either side of the crossing) but not great for locomotives. And the same issue also applies to every instance of pointwork.

toomuchtodo 5y ago

Have any resources you’d recommend for learning more about the logistics of third rail power systems? Would you happen to know what the clearance is for double stack well cars? Edit: excellent resources, thanks all for replying.

jcranmer 5y ago
The general clearance envelope you're looking at is AAR Plate H: https://commons.wikimedia.org/wiki/File:Gabarit_AAR_Plate-H.png https://commons.wikimedia.org/wiki/File:Gabarit_AAR_Plate-H....
jabl 5y ago
Third rail systems typically work at 1500V, can't go very much higher than that due to risk from arcing. Most overhead lines use 25kV, allowing much more power to be transferred, over longer distances. Which is why third rail systems are usually only seen in metro lines and similar. I'd guess in urban environments sprinkling more substations around isn't such a huge issue, as access to the power grid is seldom an issue. Also metro trains need much less power than a high speed passenger train or a heavy freight train.
- bobthepanda 5y ago
  with metros the additional consideration is tunneling. generally speaking, third rail allows for a smaller tunnel diameter than overhead systems. (third rail is located near the wider section of tunnel in the middle whereas overhead requires extending the height.)
  - bluGill 5y ago
    There are overhead rails you can use in tunnels. Nothing stops the high voltage arc issue (the whole advantage of overhead is high voltage), but without all the equipment to tension the cables you don't need as much room and the power will be one the middle of the tunnel. Anyone building new tunnel should allow the little extra room for overhead, but retrofitting may not be worth it.
danhor 5y ago
Regarding overhead wires for double stacked cars, India has a freight corridor with very high overhead wires: https://en.wikipedia.org/wiki/Dedicated_Freight_Corridor_Corporation_of_India https://en.wikipedia.org/wiki/Dedicated_Freight_Corridor_Cor... This would probably be the way to go if the US would introduce electrified rail routes. An overview of Third rail vs. Overhead Wire from a transit perspective, but it's similar with freight https://www.youtube.com/watch?v=LGI9XuHE3P0 https://www.youtube.com/watch?v=LGI9XuHE3P0 TLDR: Grade crossings are more complicated, if not impossible Smaller voltage since it's closer to the ground and the grounded rails. Thus higher current & more losses, needing more power stations. This is probably way worse for freight, since it weighs more and there are long gaps between civilization on the routes.
- bobthepanda 5y ago
  This is also already present in the US: http://2.bp.blogspot.com/-1BbF3QiAd-0/Ui9YbpGk-8I/AAAAAAAACC4/Skzmp1iCK5Q/w1200-h630-p-k-no-nu/container+clear+elec+lines.jpg http://2.bp.blogspot.com/-1BbF3QiAd-0/Ui9YbpGk-8I/AAAAAAAACC...
- pmyteh 5y ago
  Grade crossings are fine for passenger multiple units (have pickup shoes at both ends of the train and a gap either side of the crossing) but not great for locomotives. The other big problem (in addition to the ones you've outlined) is that having miles of live conductor at ground level isn't particularly safe - for track crew, trespassers, or wildlife. Britain has essentially stopped installing third rail for all these reasons. It's all 25kV overhead now.
  - iggldiggl 5y ago
    > Grade crossings are fine for passenger multiple units (have pickup shoes at both ends of the train and a gap either side of the crossing) but not great for locomotives. And the same issue also applies to every instance of pointwork.