Perhaps this is to NOT mess up the car data.
We've put some LRT rails on the Waze map here in Canada -- that way, those who ARE wazing on a train get snapped to those segments, rather than the parallel roadways.
It's not advocating using waze while on public transit... but rather, ensuring that those that do misuse it don't mess it up for everyone else.
Waze Global Champ, Mentor
Country Manager: Canada
Area Manager: Edmonton, AB; Prince George, BC; Maui, HI; Georgetown, KY and various places in between