My understanding is that the secure area in T1 is being expanded towards check-in so that a level airside pathway exists between A/Z, B and C, with Schengen on the floor level with A and non-Schengen one floor up level with Z.

The SkyTrain stations will then be able to be secure. If you arrive unclean you would go through security before riding the train, rather than the current situation of unclean train and security after getting off.

They still need to sort out the B and C mess, make it all more like A/Z, but by redoing T2 first that gives them gates to use there for when the T1 work is going to make a mess of that terminal.
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