Amtrak's Seattle-to-Chicago Empire Builder passenger train, barreling along at 70 m.p.h., jumped the tracks near the tiny town of Elmira, Ida., injuring at least 81 persons. A rail jammed into one car but missed the passengers, authorities said. All but the last car of the 12-car train left the tracks around 2:15 a.m., and six coaches, two baggage and crew cars and both locomotives turned onto their sides, said Howard Kallio, spokesman for Burlington Northern railroad. He said the train was carrying 248 passengers and a crew of 19. Kallio said it appeared that the train was traveling 70 m.p.h. at the time of the wreck.