Excerpt from CFR-2011 Title 49 Vol. 4 Part 231 FRA Rules that go back to 1911.
(d) Sill steps—(1) Number. Four.
(2) Dimensions. Minimum cross-sectional area 1⁄2 by 11⁄2 inches, or equivalent, of wrought iron or steel. Minimum length of tread, 10, preferably 12,inches. Minimum clear depth, 8 inches.
(3) Location. (i) One near each end of
each side of car, so that there shall be
not more than 18 inches from end of car
to center of tread of sill step.
(ii) Outside edge of tread of step shall
be not more than 4 inches inside of face
of side of car, preferably flush with side
(iii) Tread shall be not more than 24,
preferably not more than 22, inches
above the top of rail.Ken Adam
Thank you for posting this Ken!