[passtheglass]

I don't understand why you can't have PEDs for multiple kinds of rolling stock. That is stated but never qualified. It seems like a tractable design problem considering there are a limited set of types of train you are serving.

[Reason077]

It's not impossible, but it's difficult if the doors are different sizes and have different spacing. There are a lot of design compromises.

Here's an article about it (why Vancouver can't have PEDs): https://dailyhive.com/vancouver/translink-skytrain-station-p...

This is not really a big issue for London, though. The vast majority of London Underground platforms only have one type of train serving them. The few exceptions (eg: parts of the Piccadilly and Bakerloo lines) are mostly above ground and not the busiest parts of the network, so you could just skip the PEDs there and use manual door closing.