Copyright 2001 – 2010 Thomas C. Madden
Pullman sleepers were equipped with three-tread vestibule steps until the construction of lot 4868 in 1925. This first lot of Plan 3410A 12-1 sleepers featured four-tread steps, and these henceforth became standard equipment on all new heavyweights. Older cars rebuilt or upgraded after 1925 received four-tread steps as a matter of course.
The vestibule step data field wasn't added
Here is the difference between three-tread and four-tread steps:
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