According to safety regulations, speed signs apply to trains restricted to slower speeds by what means?

The correct answer is that speed signs apply to trains restricted to slower speeds by track bulletin, track warrant, or general order. This is important because speed restrictions are communicated through formal documentation that is part of the operating procedures in the rail industry.

Track bulletins and track warrants are specific forms of written communication that inform train crews about temporary conditions affecting the track and the speed at which their train may proceed. General orders may encompass a broader range of directives, including changes in speed due to various operational factors. Therefore, these methods ensure that all train crews are aware of and adhere to the necessary speed restrictions for safety and operational efficiency.

This reliance on formal documentation is critical in maintaining safety standards and ensuring that all train operators have the same information regarding speed limits applicable to their routes. Conversely, relying solely on one source, such as verbal instructions or informal guidelines, could lead to misunderstandings and safety hazards, hence the exclusion of those options.