(a) The skin covering the forward-facing end of a Tier III trainset shall be—

(1) Equivalent to a 1⁄2 -inch steel plate with yield strength of 25,000 pounds per square inch. Material of higher yield strength may be used to decrease the required thickness of the material provided at least an equivalent level of strength is maintained. The sum of the thicknesses of elements (e.g., skin and structural elements) from the structural leading edge of the trainset to a point, when projected onto a vertical plane, just forward of the engineer's normal operating position, may also be used to satisfy this requirement;

(2) Designed to inhibit the entry of fluids into the cab; and

(3) Affixed to the collision posts or other main structural members of the forward end structure so as to add to the strength of the end structure.

(b) Information used to demonstrate compliance with the requirements of this section shall at a minimum include a list and drawings of the structural elements considered in satisfying the thickness-strength requirement of this section, and calculations showing that the thickness-strength requirement is satisfied.