No longer accurate. See: caltrain-hsr.blogspot.com/2024/03/leve... I am not a CPUC expert but this ruling seems fairly expansive.

Level Boarding is Legal in California

Arrow level boarding platforms at San Bernardino, CA Comments to old posts on this blog are stored in a moderation queue that your author do...

Yes, this is what I meant by CPUC stating that ADA preempts their own rule. However, transit agencies are notoriously cautious about relying on rulings like this. I personally guarantee should Caltrain pursue level boarding (a big if), they will still go through the process to get a waiver.