34 Pa. Code § 25.21 – Conduct of railway personnel.

(a) Unauthorized riders. Unless properly authorized, no person whose duty does not require it shall be allowed to ride on a locomotive or train.
(b) Locomotive operation. Unless properly qualified and duly authorized, yardmasters and trainmen shall not operate a locomotive.
(c) Boarding a moving train. Trainmen shall not stand between the occupied rails to board an approaching locomotive or car.
(d) Control of trains descending an incline. When descending an incline, the engineer shall always have his train under control and be prepared to stop at any time.