The U.S. Highway System was created in 1926 to replace the inconsistently marked and maintained auto trail system. It assigned a standardized marking system for routes that crossed state lines. The route numbering system was designed to be logical, with even-numbered routes traveling east-west and odd-numbered routes traveling north-south. The lowest numbers are in the east and north, and the highest numbers are in the west and south. Although the Interstate Highway System replaced many U.S. Highways in the West, much of the system is still intact in the Eastern United States. The American Association of State highway and Transportation Officials (AASHTO) is responsible for assigning route numbers to the U.S. Highway System.