Which component primarily communicates speed restrictions to the engineer?

The cab signals are the primary component that communicates speed restrictions to the engineer. These signals provide real-time information regarding track conditions, including speed limits and any changes that may arise due to various factors such as track work or unscheduled maintenance. The cab signals are integrated into the cab of the locomotive and are designed to be visible to the engineer while operating the train, ensuring quick access to critical information without requiring the engineer to divert attention away from the track.

While other components, such as the train markers and onboard computer system, serve important roles in train operations and safety, their functions differ from the direct communication of speed restrictions. Train markers typically indicate speeds and conditions at various locations on the track, but they do not provide the same real-time feedback as cab signals. The automatic braking system can assist in controlling train speed but relies on information provided by the cab signals and other operational data. Thus, cab signals are essential for the engineer to safely manage speed limits during operation.