When may a train only ignore a red signal?

A train may only ignore a red signal when allowed by a flagger because a flagger has the authority to provide specific instructions that can override standard signal indications. This situation typically occurs in work zones or during certain operations where manual control becomes necessary for safety or operational reasons. The flagger is responsible for ensuring the safety of the crew and equipment in their vicinity, which is why their permission is critical for a train to proceed past a red signal.

The other circumstances do not provide authority to ignore a red signal as they are either dependent on changes to the signal itself (like it turning green), instructions from a dispatcher or other authority that may not specifically address the signal's indication, or the absence of other signals does not negate the requirement to obey a red signal. In all cases, the safety protocols in place prioritize the directives of a flagger when it comes to signal compliance.