in many countries, these roads are numbered to easily tell them apart. these numbered highways are usually called routes. the united states includes a system called the interstate highway system, controlled by aashto, where major north/south routes are odd numbered and east/west are even numbered. in canada, routes that are in the 400s are freeways. in china, types of routes are separated by the first letter of the route; "g" for national road, "s" for provincial road and "y" for rural roads.