You might have missed it due to COVID news coverage, but back in January 2020, whomever it is that runs BART decided to use some new taxpayer funding to replace the "50 year old" audio frequency cab signal system with CBTC. While BART does indeed have some extreme capacity constraints funneling 4 lines down a two track trunk between Oakland and Southern San Francisco, as that very city has seen with its MUNI Metro Subway, CBTC is not all its tracked up to be.
This is being brought to you by the same team that sold a $400 million combination railcar and re-signaling package to the Baltimore Metro. Hitachi purchased the Italian railcar manufacturer Breda and the Italian signal provider Ansaldo, which itself was the parent of Union Switch and Signal. I guess because Hitachi figured that Japanese engineering was better than that of Italy it has gone in with a full re-branding even though I doubt any of the actual work is being carried out in Japan. Like the DC Metro, BART has a core system that is approaching 50 years in age and likely was looking at a full signal equipment replacement similar to that which WMATA carried out after the 2009 signaling related collision. Although BART has seen many expansions over the years, its core system was and likely still is based on GRS relays and Wee-Zee bond technology.
While BART may be hoping for those 30 trains per hour, the reality will likely be less as at a certain point trains become dwell time limited. It's not that passengers can't all shuffle on and off in 30 seconds, its that they will likely not do it reliably and even a small disruption at peak capacity will result a standing wave traffic jam. Hopefully, because Bay Area, there will be some sort of backup system as you know every wanna be hacker looking to make a name for themselves will be looking for ways to disrupt the system and anything that uses wireless is ripe for disruption. If cab signal circuits will remain in service as a backup or on outer portions of the system where such equipment is not life expired, remains to be seen. The BART system was already pretty useless to railfan with dull signals and rolling stock hostile to look ahead or behind views. The new D type cars were posed to reverse this trend so get your photos and videos of the current signaling and train control before it vanishes.