When may you resume normal speed after passing a temporary speed restriction placed between mileposts?

The correct answer is that you may resume normal speed when the rear of the train clears the second milepost. This is important for ensuring that the entire train has passed the area where the speed restriction was in effect, including both the front and rear portions of the train.

The logic behind this is that to safely return to normal speed, all aspects of the train must be clear of any potential hazards or altered conditions that the speed restriction was meant to address. This means the entire train, whether it is long or short, must completely clear the second milepost to ensure that the crew can operate at normal speed without risking safety. Only upon clearing the second milepost can you safely assume that the conditions have returned to normal and that it is appropriate to increase speed.

In contrast, the other options related to when to resume normal speed do not adequately account for the entire train's position relative to the temporary restriction, which is crucial for maintaining safety standards in train operations.