The main difference between Interstate and Highway is that the Interstate is a highway system and Highway is a public or private road or other public way on land
The Dwight D. Eisenhower National System of Interstate and Defense Highways (commonly known as the Interstate Highway System, Interstate Freeways, or simply the Interstate) is a network of controlled-access highways that forms a part of the National Highway System of the United States. The system is named for President Dwight D. Eisenhower, who championed its formation. Construction was authorized by the Federal Aid Highway Act of 1956, and the original portion was completed 35 years later, although some urban routes were cancelled and never built. The network has since been extended and, as of 2013, it had a total length of 47,856 miles (77,017 km). As of 2013, about one-quarter of all vehicle miles driven in the country use the Interstate system. In 2006, the cost of construction was estimated at about $425 billion (equivalent to $499 billion in 2016).
A highway is any public or private road or other public way on land. It is used for major roads, but also includes other public roads and public tracks: It is not an equivalent term to controlled-access highway, or a translation for autobahn, autoroute, etc.
According to Merriam Webster, the use of the term predates 12th century. According to Etymonline, “high” is in the sense of “main”.
In North American and Australian English, major roads such as controlled-access highways or arterial roads are often state highways (Canada: provincial highways). Other roads may be designated “county highways” in the US and Ontario. These classifications refer to the level of government (state, provincial, county) that maintains the roadway.
In British English, “highway” is primarily a legal term. Everyday use normally implies roads, while the legal use covers any route or path with a public right of access, including footpaths etc.
The term has led to several related derived terms, including highway system, highway code, highway patrol and highwayman.
The term highway exists in distinction to “waterway”.
Of, or relating to two or more states.
Crossing states (usually provincial state, but also e.g. multinational sense).
“The truck driver drove interstate to unload.”
A Interstate Highway System.
A main, direct public road, especially a multi-lane, high speed thoroughfare connecting major population centers.
Any public road for vehicular traffic.
a main road, especially one connecting major towns or cities
“the highway to success”
“a six-lane highway”
(chiefly in official use) a public road
“the Highways Department”
a pathway connecting parts of one computer system or between different systems
“an information highway”