Given the rarity of rail accidents, and the cost of fitting seatbelts to thousands of seats, I would very much doubt it. Not to mention the impossibility of actually getting passengers to use them; I was on a local service on a brand new Oxford Bus Company vehicle the other day, fitted (to my surprise) with seatbelts, and although there was even an announcement instructing us to use the seat belts, no-one, including me, did.