What kind of trainprotection systems do they use?
I'm pretty sure the U-Bahn Hamburg doesn't have any protection system apart from Sifa. It's up to the driver to pay attention to the signals. They had tests with autonomous driving using LZB a long time ago and some DT2 and DT3 trains had the equipment for it. It was installed between Großhansdorf and Volksdorf but couldn't live up to the expectations so they removed it.