Beltway, orbital motorway, perimeter loop, beltline, and similar terms refer to an expressway/motorway/freeway style standard road that often originally enclosed the built up area and was later encroached upon by developed areas.
Ring road may sometimes refer to a beltway-style road, but more commonly indicates a road or series of roads within a city or town that have been joined together by town planners to form an orbital distributor style road, but where the standard of road could be anything from an ordinary city street up to an expressway level. The principal difference is that a ring road is an orbital distributor road system designed from already existing roads, as opposed to a beltway which is designed from new as such a road system. A ring road designation also implies a more inner-city road designed to route traffic around a city centre, as opposed to routing traffic around a larger conurbation.
Some cities have proposed or built multiple concentric beltways and/or ring roads. London, for instance, has the London Inner Ring Road (which circles Central London) and the larger M25 orbital motorway (which circles Greater London). Madrid is often cited as a pathological case, since it is served by not two, but three beltways:
Furthermore, there is a half-loop, the M-45, which runs between the M-40 and the M-50 at the east, where the two beltways are more separated; and there are plans to build a fourth full loop, the M-60, which would be over long and encompass the whole metropolitan area of Madrid. This proliferation of orbital motorways is partially due to the traditional high radiality of the Spanish highway network, which made most cross-country traffic go through Madrid.
Many beltway-style roads are part of a wider highway system, for example in the United States beltways are commonly a part of an interstate highway system. Inner/Outer labeling is a common way of uniformly signing the directions of travel on beltways in America.
Geography can sometimes complicate the construction of a beltway. One example is Stockholm, where there is a semi-beltway (Essingeleden). To be completed, most of it will have to run in submarine tunnels.