Out of interest what is a highway? I thought USA had blanket 55 MPH limit, however you say 70 MPH so it seems I am wrong.
In UK what we call a motorway is for motor vehicles only, no bikes, horses, or pedestrians, or slow moving things like tractors, other roads can have restrictions, but there needs to be a route where walkers can continue walk even if they would be silly walking down the road, so only new roads are no bikes or pedestrians.
Although both sides of the pond we speak English, there are slight differences, in the main we watch enough USA TV to know what things mean, but not all, so we have motorways with two or more lanes in each directions and hard shoulder, and in the main a central reservation, we have A roads which can be nearly as good as motorways often called trunk roads, or can be quite narrow, but still a reasonable major route, so called A road, then we have B roads which tend not to be as wide, however where a new by-pass is built often old road reclassified as B road so some of them are quite good. And we have unclassified which may not even have tarmac surface.
Odd a street can be an A road or unclassified mainly historic, so lanes, streets, byways, highways, all seem to get mixed up, bridal way for horses, motorway we have 70 MPH for cars and coaches 60 for wagons, duel carriageway also 70 MPH for cars, otherwise 60 MPH, although many roads are restricted further, unless there is a sign saying otherwise if there is road lighting it is 30 MPH in some places even down to 20 MPH.