You lost me on the cost comment.
I didn't have anything to say on that.
Metro's are nothing more than a train running underground which over time have progressed to a higher standing ratio owing to the short to moderate travel times and manage growing demand. They were built in existing cities because surface options were no longer available at reasonable cost or practical. The Inner suburban band of Sydney is closely matching this profile. Existing, high land cost, growing density to justify the higher cost underground construction costs and provide demand for high frequency services.
Classic metro, from what I know, is quite different from other heavy rail, loading gauge is always
smaller than, say, the Bern gauge. And many older metros have closer station spacing then has ever been typical of any other heavy rail including suburban rail.
In older global cities, options for surface rail into the town centre were never available, having been developed before the railways came, and regional trains, being steam hauled, could not run underground, and all trains at that time were single decked. Also, I don't believe that modern tunnel boring machines existed yet.
All our state capitals, being late developers, all have surface rail running right into the CBD. This was impossible in older cities for reasons mentioned above, so metro was seen as a way to get people between town centres and rail stations on the outskirts.
Both Melbourne and Sydney later electrified their surface rail, which, first in Sydney and later in Melbourne, to a lesser extent, allowed suburban services to be extended underground.
For all I know, regional rail in Europe was still (largely) unelectrified when now legacy metros were first opened.
The most common reason for being non-interoperable is because they take advantage of the latest technology. There is no need or no benefit or most commonly simply no capacity to mix trains from one line to another without causing the problems Sydney has. If the trains are manually driven, the drivers don't need to be trained for every piece of track in the city, just A-B-A and maybe one or two other lines. Sydney has progressed down this path over last 10 years and now I see now comments that Mel Metro operator is looking at following a similar path.
Whatever it is, I doubt there would be a reason to remove any productivity features on the new line.
Again relevance of who came first in most circumstances? Paris has seen more extension of RER because the city is growing out. There are height limits on buildings in inner Paris so the population growth is limited. And as someone pointed out, Line 14 was to ease congestion on a RER line.
Remember, it isn't just Paris, someone else pointed out that London has also seen more extensions to the overground than recent extensions to the underground.
And proven to cause more problems long term than it solved and very much short sighted leaving the problem for others to solve in the future, again!
I haven't heard that as a reason for changing plans.
No, the train cross sectional area is aligned with similar systems built around the world today.
Far from it, there are a variety of loading gauges around the world, mainland Europe and North America and larger than the British Isles, and here in Australia there are a number of variations, including differeces between Melbourne and Sydney suburban.
Link doesn't work and your words were "same frequency", again you need to take your thinking out of the DD box. I said technology frequency. ie DD at 2.5min and SD at 1.5min.
I clicked on the link and it does work. Accrding to Douglas Economics, existing signalling allows 20 double decker or 22 single deckers an hour, while enhanced signalling will allow 26 single deckers or 24 double deckers in the same amount of time.
My point is that there is no way around the fact that a larger loading gauge such that double decker trains will fit is a productivity feature.
Tolerated? So you telling me if I went to Paris or German cities and asked how do you feel that you are in this SD car verus those in the DD cars, you are not getting your monies worth? I wonder back when Sydney was running mixed trains of SD/DD red rattlers if those in the DD trailer cars felt more superior to those in the SD cars. Do those sitting up the top feel superior to those in the lower decks?
I don't understand the first part of the first sentence, but Sydney ran those mixed trains on the same network, and I've read that the RER still has both, though progressively phasing out single deckers.
So let's consider here:
London - underground and overground, both with single deck trains only.
Paris - metro, with small bore tunnel and single deck trains only, and RER, originally with only single deck trains, but now, newer trains are double decked.
Both these cities already had extensive metros with the small bore tunnels in place, such that it would be too expensive and inconvenient to enlarge the tunnels and consolidate stations. It simply wouldn't be worth undertaking such expenditure and inconvenience for the benefits obtained.
It would be a bit like giving someone a foot transplant and go into the trouble of getting them walking again just because the shoes that fit their new feet are more comfortable.
That's what I mean by tollerating the metro-suburban divide. It's no more than a product of having a metro in place when suburban rail began, and the infeasibily of integrating it into the suburban rail network.