Firstly, the average is irrelevant when specifying minimum clearances - it would be stupid to make a cutting deeper just to let the railway go under a bridge at average clearance.Will409 wrote:For 25000 kV 50Hz AC electric traction like what we are getting, the average height of the contact wire (in Queensland atleast) is 1m above the roof of the rollingstock. That is only the contact wire, the additional wiring and caternary structures stand even higher so a fair amount of above head clearance is needed. The width of the alignment generally also needs to be wider to take the caternary masts also. Finally, it does help having and alignment with light gradients and curve radius to allow for higher speeds. Sometimes it is better to over engineer things.
Secondly, how much more do you think it's worth paying to design a passenger railway to freight standards, including double stacking of containers (depite the loading gauge N of Noarlunga being inadequate for that)?
Thirdly, while you are correct about curve radius, light gradients should not be necessary for electric railcars to perform well, especially where (due to station location) they'd be accelerating on a down gradient and decelerating on an up gradient.
Fourthly, yes, sometimes it is better to overengineer things - but this isn't one of those times. When you don't know what the future requirements will be, the Bazalgette principle applies. But in this case we have a pretty good idea of what future requirements will be. And while it makes sense to make provision for the future (e.g. put stations on a straight section at least 300m long to make it easier to extend the platforms) it does not make sense to blow the budget on features that are unlikely to ever be needed.
When London's Piccadilly Line was extended to Heathrow Terminal 4, provision was made for Terminal 5, so the trains went round an unnecessarily large loop (from T4 to T123 via the proposed T5 site) for about 20 years. Meanwhile plans changed, and Terminal 5 was eventually built further W. So remember, spending extra money is not always productive!
BTW I have raised my concerns with DTEI.