This happened to me about six years ago. I was on a Metroliner during winter weather and I believe the engine crapped out. Another Metroliner pulled up next to us and we walked down the vestibule steps, across the ballast, and up onto the other train. I don't know if there were any disabled pax. But I did hear that Amtrak is buying new bridge plates that will allow train-train transfers with no steps required.