8b9da35c_s___Travel_guide_at_Wikivoyage__UK
[US] highway/freeway/expressway/limited-access road [Notes] "Interstate" is the name of a specific U.S. highway system. In actual parlance many Americans use the name or rather number of a street when referring specifically to it (e.g. [the] I 45, Route 66 etc.) [UK] 
motorway
English language varieties – Travel guide at Wikivoyage
UK