Thanks again thewaratahtrain and to others who have since responded.
I did already know about the Yanchep extension of the Joondalup line, it has been discussed in one form or another for quite a while, but it is probably worth having a record of where that stands at the moment in this thread. Another recent reliable publicly available source for that is the Public Transport for Perth in 2031
report. It recommends that extension as a Stage 1 (ie by 2020) priority "extension of the Northern Suburbs Railway from Butler to Yanchep with stations at Alkimos, Eglinton and Yanchep (13.8kms)" As for the Mandurah line the same report mentions "new stations and interchange facilities on the Mandurah line at Success and Karnup." That is the recently announced Aubin Grove and a station to serve the future Keralup development and nearby growing suburban catchment. But before going further into plans for extending the lines or adding stations I was interested in this notion of platforms for nine-car sets arising from the quote that thewaratahtrain found.
@ Bulbous - A rail corridor as far as Moore River? That is seriously a long way. I know the MRS plan shows something going beyond Two Rocks (it disappears at the edge of the map), are there easily accessible documents showing the further extension? I imagine the alignment has changed a lot over the years. I completely agree that the short term goal should be an increase in frequency of six-car sets on these lines before considering nines (if they are even possible,) and I would have thought that was the priority of the PTA. (One of the positive comments from the Federal Govt Understanding Australia’s Railways
report is that the frequency of off-peak services in Perth has contributed to the success of the system.) That is partly why I was so surprised to hear of this long platform being built now. Also the PTA Annual Report for 2010/11 suggests that the existing Joondalup line infrastructure has the capacity to take up to 20 six-car sets an hour in peak periods (this matches your comment mouse), up from around twelve sets an hour at peak now. So again, building a nine car platform now sounds a little premature.
@ 62440 - You mention several of the probable future stations on the Mandurah line, I think that the one you refer to as Russell/ Gibbs is the announced Aubin Grove and the one at Paganoni Rd is referred to as Karnup in a couple of recent government reports. Rowley Rd, Ankatell Rd and South Perth are all clear candidates for future stations from both rumours and aerial photos. Stakehill Rd and Gordon Rds are less obvious (planned stations without island platforms are not as clear on Google Earth!) I would be interested if you know if there is any documentation to confirm all of these.
But premature or not, the potential for expansion to nine-car sets is what is interesting me at the moment given the recent quote from Troy Buswell regarding Aubin Grove. I would still love to know if there is anyone who was directly involved in the planning and design of these lines and their stations who can comment on the possible provision for longer platforms, or if there is documentation in the public domain to the same effect. 62440 and waratah have both highlighted the apparent problem with the Perth Underground and the Esplanade which I'm sure we can all see, but it still leaves me wondering if there is something planned that we can’t see. Otherwise why would they be building a platform to suit a nine-car set now? That is the big mystery of the moment.
And @ Bulbous again (this thread is being added to before I have time to finish considering a response) thanks for your firsthand insight into the Perth Underground construction. Just as you mentioned a void that was built that Joe Public can’t see now, I was wondering if there was some design provision made for platform extension that is less than obvious.
@ drwaddles, Bulbous & 62440 - The crossover mess? Now we could be getting into the short-sightedness of not spending a bit more to keep the Joondalup - Mandurah connection below ground from the start and allow for future lowering of the Freo line. 62440 is right, obviously too late and costly to change now, and building over it is I believe what is proposed as part of the Perth City Link project. I could rant on but that could be going off topic. I'm just thankful that a change in government at the time helped to find the cash to bring the Mandurah line over the Narrows Bridge instead of going via Kenwick.
And finally since I have only made a couple of posts on here prior to starting this thread, I feel that I should apologise for my interest in quotable sources for information. I've been lurking here for a several years now and I've seen many unfounded rumours come and go. I enjoy speculation as much as the next person, but sometimes it is good to sort the reality from the dreams. Although of course dreams do have their benefits. Now I need to send this before i fall further behind in reading comments.