From: ce11son@yahoo.ca   
      
   On Thu, 19 Jun 2014 15:45:33 -0700, Nobody  wrote:   
      
   >On Thu, 19 Jun 2014 21:54:09 +0100, Charles Ellson    
   >wrote:   
   >   
   >>On Thu, 19 Jun 2014 10:23:38 -0700, Nobody  wrote:   
   >>   
   >>>On Thu, 19 Jun 2014 00:00:19 +0200, 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.   
   >>>   
   >>>I've wondered how Yarra Trams in Melbourne handles that situation,   
   >>>where its system crosses tracks of the region's electrified heavy-rail   
   >>>network.   
   >>>   
   >>There is a description in :-   
   >>http://en.wikipedia.org/wiki/Trams_in_Melbourne   
   >>(Tram/train level crossings)   
   >>The mechanical bit is probably the simple part of the design with the   
   >>electrics requiring various interlockings so that the appropriate   
   >>single voltage is applied to the entire assembly above the crossing to   
   >>match the "open" route. This only goes up to 1500v which is possibly   
   >>not that disastrous for the trams if it is accidentally applied in the   
   >>short term but ISTR there are (or used to be) installations in   
   >>continental Europe involving 15kV or 25kV on the railway;   
   >>http://railforthevalley.wordpress.com/2010/05/11/when-trolleyb   
   s-and-streetcar-cross-paths/   
   >>mentions Suhr in Switzerland (1200V DC v. 15kV AC) and has a   
   >>photograph of a train/trolleybus crossing in Russia.   
   >>   
   >>http://www.youtube.com/watch?v=v_hNE2NUbCE shows one of the Melbourne   
   >>level crossings including another necessary feature of hingeing the   
   >>half-barriers to prevent them touching the tramwires.   
   >>   
   >   
   >Thanks.  The Mellie isolation section makes sense, even to me!  It's   
   >interesting that the trams run with the panto elbow facing to the   
   >rear.   
   >   
   Assuming the route doesn't have a turning circle at each end (the   
   trams are double-ended with a single pantograph), I think that's just   
   how those two happened to arrive.   
      
   >And in looking at all the info you pointed to, it reminded me that   
   >Wellington, NZ's last few tram routes co-existed with the city's large   
   >trolley bus network in the 50's and early 60's, especially as they   
   >were (still are) concentrated on four major streets in the CBD.   
   >   
      
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