In regard to dynamic brakes, what does a + symbol indicate in the axle rating?

The + symbol in the axle rating indicates that the dynamic brake rating exceeds the actual number of axles. This is significant because it reflects the locomotive's ability to generate additional braking force beyond what might be expected based on its axle configuration. Enhanced dynamic braking capabilities can be crucial for controlling speeds, especially on descents, where extra braking power aids in maintaining safe operational limits.

This understanding reinforces the importance of dynamic brakes in train operation, particularly under conditions where conventional air brakes alone might not provide sufficient stopping capability. Recognizing the connection between the axle rating and dynamic braking performance can help train operators make informed decisions about safety, efficiency, and performance during various running conditions.