The first Superliner I cars entered service in February 1979, with deliveries continuing through 1981. Amtrak assigned the cars to both long-distance and short-distance trains in the Western United States. The first permanent assignment, in October 1979, was to the Chicago–Seattle "Empire Builder". Superliner II deliveries began in 1993; the additional cars enabled the retirement of the aging Hi-Level cars and the assignment of Superliners to trains in the Eastern United States. Tunnel clearances prevent their use on the Northeast Corridor.