The Janney coupler is a type of automatic coupling device used primarily in rail transport. It allows train cars to connect and disconnect easily without requiring manual intervention. This system enhances safety and efficiency, as it reduces the risk of accidents during coupling operations. Developed in the late 19th century, the Janney coupler became a standard in the United States, replacing older coupling methods. Its design includes a knuckle mechanism that securely locks the cars together, making it a reliable choice for both freight and passenger trains. The coupler is often referred to as the AAR coupler due to its adoption by the Association of American Railroads.