How accurate must locomotive speed indicators be within?

Locomotive speed indicators are required to maintain a specific level of accuracy to ensure safe operation. The correct response highlights that these indicators must be accurate within ±3 MPH at speeds between 10 and 30 MPH. This range is particularly important because it represents a critical operational speed where the performance of the locomotive can significantly impact safety and efficiency.

At lower speeds, such as those below 10 MPH or at a standstill, the accuracy tolerance can be less stringent, as the risk associated with small discrepancies in speed measurements is lower. Conversely, as the speed increases above 30 MPH, the acceptable error range becomes ±4 MPH, acknowledging that the factors involved in speed measurement can become slightly less precise at higher velocities while still maintaining safety standards.

In summary, the accuracy requirement of ±3 MPH for speeds between 10 and 30 MPH reflects a careful balance between operational safety and the realities of measuring speed in dynamic conditions. It ensures that operators receive a reliable indication of speed critical for controlling the locomotive effectively.