The brake dust from low-noise train brakes smells so incredibly nasty (burning ABS, pretty much) but the operators and OEMs claim it’s <<safe>>. Bonus points for the Bombardier bi-level coaches, where the AC air intake is right above the wheelsets and takes a healthy gulp of that brake dust and smell and distributes it to the passengers inside (because the smell is just as pungent inside as outside a few seconds after coming to a stop I doubt the filters, if any, are doing much). Frankly I’d not commute with it.