On recent long-haul trip on Acela I seem to recall low 1,000s PPM (65% full train across 7hr trip). On a regular train trip, a bit higher, like 1,250-1,900 PPM

On recent long-haul trip on Acela I seem to recall low 1,000s PPM (65% full train across 7hr trip). On a regular train trip, a bit higher, like 1,250-1,900 PPM on a fairly packed train (10 hr trip). Both northeast corridor.