49 CFR § 214.518
Safe and secure positions for riders
November 18, 2020
On or after March 1, 2004, a roadway worker, other than the machine operator, is prohibited from riding on any on-track roadway maintenance machine unless a safe and secure position for each roadway worker on the machine is clearly identified by stenciling, marking, or other written notice.
[69 FR 8839, Feb. 26, 2004]