Comment by bdb

Pure speculation on my part, but given the limited suitable equipment space available in each BART station, it's likely that BART has deployed a neutral host (i.e., BART-owned, not carrier-owned) distributed antenna system[1] throughout their stations. In that case, it's easy for them to cut power to the actual RF gear without carrier intervention (and without having to worry about those pesky strings of 48V batteries keeping things running.)

The bigger issue to me is that is almost certainly illegal to willfully disrupt 911 service, and it's unlikely that whoever flipped whatever switch, be it disrupting commercial power to carrier-owned base stations or a BART-owned DAS, was able to disrupt texts/voice calls to other parties selectively without disrupting 911 service.

[1] http://www.infinigy.com/PDF/InfinigyNeutralHostWhitepaper.pd...