In Big cities, migrating from one end of the city to another by means of ordinary streets and avenues can be time-wasting since traffic is often slowed by at-grade junctions, tight turns, narrow marked lanes and lack of a minimum speed limit. Therefore, it has become common practice for larger cities to construct expressways or freeways, which are large and wide roadways with limited access, that typically run for long distances without at-grade junctions.
The words expressway and freeway have varying meanings in different jurisdictions and in popular use in different places; however, there are two major different types of roads used to provide high-speed access across urban areas:
• The freeway (in U.S. usage) or motorway in UK usage is a divided multi-lane highway with fully-controlled access and grade-separated intersections (no cross traffic). Some freeways are called expressways, super-highways, or turnpikes, depending on local usage. Access to freeways is fully controlled; entering and leaving the freeway is allowed only at grade-separated interchanges.
• The expressway (when the name does not refer to a freeway or motorway) is usually a broad multi-lane avenue, frequently divided, with some grade-level intersections (although usually only where other expressways or arterial roads cross).
Motor vehicle drivers intending to travel over great distances within the city will usually take the freeways or expressways to minimize travel time. When a crossing road is at the same grade as the freeway, a bridge (or, less often, an underpass) will be built for the crossing road. If the freeway is elevated, the crossing road will pass underneath it.
Minimum speed signs are sometimes posted (although increasingly rare) and usually mean that any vehicle traveling slower than 40 mph (64 km/h) should indicate a slower speed of travel to other motor vehicles by engaging the vehicle's four-way flashing lights. Alternative slower-than-posted speeds may be in effect, based on the posted speed limit of the highway/freeway.
Systems of freeways and expressways are also built to connect distant and regional cities, notable systems include the Interstate highways, the Auto-bahnen and the Expressway Network of the People's Republic of China.