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==== Highway systems ====
[[File:Autostrada del Sole - Italy - panoramio.jpg|thumb|[[Autostrada A1 (Italy)|Autostrada A1]] runs through [[Italy]] linking some of the [[List of cities in Italy|largest cities of the country]]: [[Milan]], [[Bologna]], [[Florence]], [[Rome]] and [[Naples]]]]
In many countries,{{which}} the controlled-access highways form an expansive system that generally connect distant cities within the country to each other, but there are often more highways that only have local courses designed to improve connections in a smaller region, such as within a metropolitan area.{{Clarify |date=April 2025 |reason=There are also many countries with top-level highway systems with few, if any, controlled-access highways. Limited access highways are more universal.}} Controlled-access highways are often given numbers to form a national highway system, such as the ''[[Bundesautobahn]]'' in Germany or the [[Interstate Highway System]] in the United States, but note that a national highway system may also consist of other numbered highways that are not implemented as controlled-access highways. Some countries may have more than one national highway system of a lower rank, such as the [[U.S. Highways]] (not to be confused with the Interstate system), only portions of which run on controlled-access highways. Conversely, there may also be controlled-access highways not part of a numbered system. Highways are usually given icons featuring the number of the highway called [[Highway shield|highway shields or route markers]]. In addition to the national highway system, there may be provincial-level or state-level (US) highway systems of a lower rank, which need not consist mainly of controlled-access highways.
Slip roads (UK) or ramps (US) are special connector roads that allow traffic access to and from a controlled-access highway. Their length is normally on the order of several hundred meters in order to allow vehicles a sufficient distance to safely change speed while transferring from one road to the other road. The course of a ramp is often curved as needed in order to connect the two roads without sharp turns, which require vehicles to slow down considerably to traverse them safely. In many cases, a ramp may be subject to grade separation and use a flyover. In the US, where the standard term for a flyover is ''overpass'' (or ''underpass'', when the road with level altitude is the higher road), the word ''flyover'', which is less common, is reserved for those that carry ramps. Entrance ramps (or on-ramps) allow ''ingress'' traffic to enter the highway, and exit ramps (or off-ramps) allow ''egress'' traffic to exit the highway.
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