[bobthepanda]

> CBTC was supposed to increase capacity on the L

This is not strictly true. CBTC was put on the L first since, at the time of procurement in 2004, it was an ideal testbed as a moderate-ridership, fairly long line isolated from the rest of the system.

It was not immediately obvious that the L would become the center of gentrification in the late 2000s and 2010s; in the '70s and '80s it had such low ridership that they were proposing its closure. So they only ordered enough train cars to meet the 2004 ridership demand.