Which of the following denotes a method for restricting train access?

The correct answer focuses on "Inaccessible Track,” which denotes a method for restricting train access. This term implies that certain segments of the tracks are not available for train operations, often due to maintenance work, repairs, or conditions that make the track unsafe. By declaring a track as inaccessible, the railroad ensures that trains cannot enter these sections, thereby preventing accidents and ensuring the safety of both personnel and equipment.

While the other options relate to train operations or information, they do not specifically refer to restrictions on train access. An operating schedule outlines when trains are expected to run, but it does not inherently restrict access to any tracks. Controlled track refers to sections of track that are managed with specific rules or signals, but it does not imply restriction like "inaccessible" does. A summary bulletin order provides vital operational information but is primarily a means of communication rather than a direct restriction on track access. Thus, "Inaccessible Track" effectively represents the concept of restricting access to train operations.