In the United Kingdom, the Republic of Ireland, Hong Kong and Commonwealth countries such as India, South Africa, Australia and New Zealand, a subway is normally an underpass for pedestrians and/or cyclists beneath a road or railway, allowing them to reach the other side in safety. Subways may also be constructed for the benefit of wildlife.
In the United States, as used by the California Department of Transportation and in parts of Pennsylvania such as Harrisburg, Duncannon and Wyoming County, it can mean a depressed road undercrossing.
Subways are less common in North American cities than in European cities of comparable size. They are constructed when it is necessary for pedestrians to cross a railway line or a dual carriageway such as an interstate highway, and they appear at the exits from underground rapid transit systems, but one would be rarely built to enable people to cross an ordinary city street. When they are built, the term pedestrian underpass is more likely to be used, because "subway" in North America refers to rapid transit systems such as the New York City Subway or the Toronto Subway. This usage also occurs in Scotland, where the underground railway in Glasgow is referred to as the Glasgow Subway
In the Philippines, the term is also underpass, and there are two types: underpasses for pedestrians such as along Ayala Avenue in Makati and in the City of Manila near Quiapo Church, and vehicular ones along the length of EDSA and other thoroughfares. One of the earliest and most notable vehicular underpasses is the "Lagusnilad" in front of Manila City Hall.
A subway road sign (ex-USSR)
A subway in Ashgabat
A pedestrian and cyclist subway under a roundabout in Cardiff, Wales
A subway in Hong Kong leading to an underground MTR station and shopping centres
The entrance to a subway in Saint Petersburg
A frog subway
Subway connecting Red and Blue "subway" lines in the Loop area of Chicago
Victorian era pedestrian subway under a railway at Godalming in the United Kingdom, built in 1859
A pedestrian tunnel in Louvain-la-Neuve