>>1845483they still end up mixing local and express S-Bahnen or just have very long local lines. They need more capacity at Stadelhofen and Hardbrücke first. That was a cheapskate solution back then to have just 3 tracks in Stadelhofen.
And swapping Sihltalbahn to single deck EMU trains should be a nobrainer because of better acceleration instead of that funny mixed rolling stock they have.