[jdblair]

You are correct that this would be much simpler if the only goal was to replace the floppy disk part of the system.

The floppy disk angle is there to make a good headline. The article makes it clear this is a much bigger project than just replacing the floppy disks.

  "The detail[ed] project schedule will be finalized once we have a contractor onboard. This is effectively a multi-phase decade long project that starts with pieces of market street subway and pieces in the surface. Ultimately our goal is to have a single train control system for the entire rail system," said Tumlin.

[renewiltord]

SF has to make everything a big bang project because every project has equal large fixed cost. So whether you do a small thing or a big thing you do a big fixed cost thing first.

So SF always does the big thing because otherwise the overhead dominates.