september.org> 52E9FFA6   
   From: marc.gr.vandyck@invalid.skynet.be   
      
   bob brought next idea :   
   >   
   > I do wonder the extent to which power independence is useful for a tram,   
   > though. On a trolleybus, the utility is clear, but if you need tracks to   
   > run a tram on, the restrictions of being tied to an overhead wire are not   
   > significant. The only use case I can see for them is in locations where the   
   > visual intrusion of overhead power is undesirable.   
   > Robin   
      
   A second possible usage is at crossings between different transit   
   systems, for example a tram line and a trolleybus line. The needed   
   insulation between the wires makes such crossings quite complex, and   
   it is now easier to give the trams some independence from the overhead   
   wire, so that they can lower the panto before the crossing and raise it   
   back after. This way, the tram wire can simply be interrupted at the   
   crossing and the complexity is eliminated.   
      
   Another case is for passing under short tunnels or bridges, where there   
   wouldn't be enough free height to install the overhead wire + required   
   insulation distance. Get the trams under there on their own power and   
   the problem is solved...   
      
   Then you have the places where trams are stored and maintained, which   
   require also complex overhead wire installations, which can totally be   
   eliminated if the trams can move independently.   
      
   Also, because of the low floors, the technical equipment on last   
   generation trams is often on the roofs, which means maintenance shops   
   must be equipped with platforms from where this roof-mounted equipment   
   is easily accessible. Such platforms require sophisticated safety   
   equipment to ensure noone can be on them if the overhead wires are not   
   switched off and grounded. If the trams can move to those platforms on   
   their own power, the wires can simply be eliminated.   
      
   --   
   Marc Van Dyck   
      
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