Yup, no doubt about it, you do “descend from a vehicle” when you alight the train. But have you ever heard anyone, other than an employee of a train company, use this verb? Most of us “get off” trains.” Tell someone you’re alighting at the next station for a puzzled look behind a face that longs to ask “Do you really talk like that?”
It reminds me of directions printed in the Bradford South billiards’handbook in the mid-1970s. “Alight Busby’s” advised the booklet. The famous city department store, by this time closed, burnt down shortly after publication