What is the maximum allowed speed for Class 3 track with a 3/16" tread mismatch?

The maximum allowed speed for Class 3 track with a 3/16" tread mismatch is 40 mph. This standard is set to ensure safety and operational efficiency when there are discrepancies in the dimensions of wheel treads that could affect the stability and integrity of trains traveling on the track.

In railway operations, the classification of track types (Classes 1 through 6) corresponds to specific maximum speed limits based on track condition, geometry, and clearances. Class 3 track is designated for speeds up to 40 mph under normal conditions. When a tread mismatch occurs, it's crucial to adhere to stricter speed limits to prevent derailment or other safety issues that could arise from the uneven distribution of weight and stability of the train's wheels.

In this context, any higher speed limits would not be appropriate, as they could compromise the safety of rail operations under those specific conditions. Thus, the correct answer reflects a balanced consideration of safety and operational protocols.