Skybridge

A skyway, skybridge, or skywalk is a type of pedway consisting of an enclosed or covered bridge between two or more buildings in an urban area. This protects pedestrians from the weather. In North America skyways are usually owned by businesses, and are therefore not public spaces (compare with sidewalk). However, in Asia, such as Bangkok's and Hong Kong's skywalks, they are built and owned separately by the city government, connecting between privately run rail stations or other transport with their own footbridges, and run many kilometers. Skyways usually connect on the first few floors above the ground-level floor, though they are sometimes much higher, as in Petronas Towers. The space in the buildings connected by skyways is often devoted to retail business, so areas around the skyway may operate as a shopping mall. Non-commercial areas with closely associated buildings, such as university campuses, can often have skyways and/or tunnels connecting buildings.

The world's largest discontinuous skyway network – Calgary, Alberta's "+15 Walkway" system – has a total length of 18 km (11 mi). The Minneapolis Skyway System is the world's largest continuous system and spans 8 miles (13 km) connecting 69 blocks in downtown Minneapolis.

On a smaller scale, terminals of large airports are often connected by skywalk systems, as at Manchester Airport, United Kingdom.

Some cities have the equivalent of a skyway underground, and there are also mixed subway/skyway systems; see underground city.

Besides pedestrian safety and convenience, the chief reasons assigned by urban planners for skywalk development are decrease of traffic congestion, reduction in vehicular air pollution and separation of people from vehicular noise. A number of cities (for example, Spokane, Washington) have given intricate analysis to skywalk systems employing computer models to optimize skywalk layout.

...
Wikipedia