If a freight train has 90 or more cars or tonnage of 80 percent or more, what may it do concerning signals with a yellow disc?

The correct choice indicates that a freight train with 90 or more cars or a tonnage of 80 percent or more is allowed to proceed at restricted speed without stopping when encountering signals displaying a yellow disc. This rule is designed to facilitate the movement of longer or heavier trains while still maintaining safety protocols.

"Restricted speed" allows trains to operate in a manner that enables them to stop within half the range of vision, as well as to ensure that they can respond appropriately to equipment or track conditions. This rule acknowledges the operational characteristics of larger freight trains, which may be challenging to stop quickly due to their size and weight. Therefore, allowing them to proceed under these conditions streamlines operations while keeping safety at the forefront.

It’s important to remember that this practice is specifically tied to the performance capabilities of freight trains, ensuring that while they can move without stopping at signals, they must still adhere to safety protocols that restrict their speed to a manageable level.