49 U.S.C. § 20501: Definition

In this chapter, “signal system” means a block signal system, an interlocking, automatic train stop, train control, or cab-signal device, or a similar appliance, method, device, or system intended to promote safety in railroad operations. Not later than 18 months after the date of enactment of this Act [ Dec. 4, 2015 ], the Secretary [of Transportation] shall initiate a rulemaking to require that on-track safety regulations, whenever practicable and consistent with other safety requirements and operational considerations, include requiring implementation of redundant signal protection for maintenance-of-way work crews who depend on a train dispatcher to provide signal protection. The Secretary shall consider exempting from any final requirements of this section each segment of track for which operations are governed by a positive train control system certified under section 20157 of title 49 , United States Code, or any other safety technology or practice that would achieve an equivalent or greater level of safety in providing additional signal protection.”