49 CFR §214.335

1. (a)No employer subject to the provisions of this part shall require or permit a roadway worker who is a member of a roadway work group to foul a track unless on-track safety is provided by either working limits, train approach warning, or definite train location in accordance with the applicable provisions of § 214.319, § 214.321, § 214.323, § 214.325, § 214.327, § 214.329, § 214.331, or § 214.336.
2. (b)No roadway worker who is a member of a roadway work group shall foul a track without having been informed by the roadway worker in charge of the roadway work group that on-track safety is provided.