What should be used to advise a train dispatcher of a restriction?

Using mile posts and tenths of a mile from the posts is the correct method for advising a train dispatcher of a restriction because it provides precise and universally understood location references on the railroad. Mile posts are established markers along the track that indicate specific distances from a designated starting point, often used in conjunction with tenths of a mile for added accuracy. This system ensures that all parties involved in train operations can quickly and accurately identify the location of a restriction, which is crucial for safe and efficient train movements.

The other methods, although potentially useful in other contexts, do not provide spatial reference as clearly or universally as mile posts do. Signal patterns and codes may convey various operational messages but are less specific regarding geographic location. Coordinates could be used as another way to denote a location, but they require additional interpretation compared to the simplicity of mile post references and can vary in format. Direct communication via radio is effective for real-time updates but may lack the necessary context without a defined location to refer to, which mile posts clearly provide. Thus, using mile posts enhances clarity and facilitates accurate communication in the operating environment of railroads.