Edited 03 Dec 2017 07:21, 3 years ago, edited by Myrtone

For one, they don't build DD trains to give more pax, crush loading is based on floor space and seating capacity. Remove the seats and you have more standing capacity and more capacity on the train. Dubai like many cities running train frequencies based on loading factor and the train technology is irrelevant.

I don't get this distinction. Train technology does affect capacity.

While most govts tolerate bikes on their trains, one bike takes up the space of two pax and can add significantly two dwell times to get on and off crowded trains and platforms as well as significant safety issues, hence why restrictions are in place in many cities.

Let me tell you something; Bicycles take up less space than wheelchairs. And bicycles can be stored vertically and take up even less space.
You suggested that even double deckers might not be large enough to carry bicycles as well as passengers, so making the platforms longer and using longer trains would leave enough space for them.

No comment on the standards to which the metro is being built.

Sydney has a number of lines all stations to the city (from outer suburban) with no express running due to traffic density. There will be more in the future as the population increases unless extra capacity is built.  The use of using one pair of tracks to run both express and local is a hang up of the past. As in most cases the corridor width is full thus forcing more complex and costly issues such as tunnelling as is happening. The issue being that these corridors are not short, rather 10's of km long thus making these project multi billion dollar projects and adding even 0.5m extra width to the tunnel can add hundreds of millions of dollars to a project.

Maybe on the North Shore line but there's lots of Quaruple track on the south side so express trains wouldn't need to share the same pair of tracks as all stations trains.

You say DD is expanding, I only see DD commuter networks expanding in a very limited number of locations and not being used for inner suburban expansion and upgrades. For every new DD carriage that is being built, there is probably at least one train set of SD fully Automated that is being built. China built how many new lines in last 20 years, how many are ?

Double deckers are indeed being depolyed on all the busiest regional and suburban rail networks where they will fit. Look at Belgian National Railways, Luxembourg state railways, Russia's Aeroexpress, the German state of Brandenburg (which surrounds Berlin), and Zuerich's S-bahn, and Switzerland's other suburban rail network, in Bern.
And get this, the Luxembourg, Brandenburg and Zuerich orders are all for the same train model - from Stadler. The Russian order is for a Soviet gauge variant.
If a single decker from a European supplier built for an Australian legacy system only needs to be lightly customised, why should a double decker from the same supplier be more so.

No comment on the rest.