This is the thing, The USA uses the title "Major Highway" as a grouping, and then has sub treecategoriesthat come off it. Nothing points to 'Major Highway' as being its own entity. I would assume that Interstates and numbered highways are what is classed as major highways, the remainder are carriageways, A & B roads.
Definition : Major Highway
a major roadway thatcarrieshigh volumes of traffic; the breakdown of which in descending order is:
<b style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 13px; : rgb239, 239, 239; max-width: 690px; line-height: normal;">Interstates[/b](90/10 federal/state financing),
<b style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 13px; : rgb239, 239, 239; max-width: 690px; line-height: normal;">US-numbered highways[/b](50/50 federal/state financing);
<b style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 13px; : rgb239, 239, 239; max-width: 690px; line-height: normal;">state roads[/b](no federal, state funding only) and
<b style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 13px; : rgb239, 239, 239; max-width: 690px; line-height: normal;">local roads and streets[/b](local financing only)
(Source Site -
http://www.springerreference.com/docs/html/chapterdbid/196158.html)
Sorry, best I can do for you