september.org> B6222FA2   
   From: rcp27g@gmail.com   
      
   Marc Van Dyck  wrote:   
   > 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.   
      
   There are numerous crossings between tram and trolleybus overhead on the   
   Zürich systems, and frankly the junctions are not particularly complex   
   where the tram and trolley uses both operate at a similar voltage.   
   Certainly it is no more complicated than a regular turnout on a trolleybus   
   overhead. The complexity needed to actually terminate the tram overhead on   
   both sides of a junction with a gap through it would likely be more than   
   required for a conventional crossing. Even if you have the tram overhead   
   through the junction as a neutral section, unless the junction is really   
   badly designed, an unpowered tram should be able to coast through, he   
   rolling resistance for a tram is pretty low.   
      
   Robin   
      
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