In NYC, faster-accelerating subway trains, with not-better brakes, actually caused slower subway service. The coarse-grained signaling had to assume the worst case: a subway train that started max acceleration (operator fainted on gas pedal?) just after a signal, and wouldn't have emergency brakes automatically tripped until the next signal. So faster accelerating cars can get faster in that segment, and require keeping more signal-blocks of spacing between trains for max emergency braking distance. (So, really the fault of old signals and brakes, but still, faster trains had slower service :) https://homesignalblog.wordpress.com/2022/12/21/how-we-slowe...