What about inflexibility?  This year the Overland has typically run at
5 or 6 cars, yet on days of big football matches in Melbourne with
Adelaide teams playing it operates with more than twice that number.
If you run XPTs you totally remove the ability to add cars, and these
days extra trains just don't appear.
Cheers...JD
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John Dennis                         jdennis@acslink.net.au
Melbourne                                  denjo02@cai.com
Australia               http://www.acslink.net.au/~jdennis
               Dutton Bay Tramway pages updated 1 November