Elephant Underpass, Kenya, Africa,

Underground pedestrian passageways 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 railroad or a limited-access highway such as an interstate highway, and of course they appear at the exits from underground rapid transit systems, but one would be rarely built just to enable people to cross an ordinary city street. When they are built, the term pedestrian underpass is more likely to be used, since the word "subway" is usually used there to refer to rail-based rapid transit systems such as New York Subway in the United States.
In the Philippines, it can be seen in the city of Makati and some places in Manila, such as in Quiapo and near the Manila City Hall, commonly known as "Lagusnilad."
Subways used to be widely built in countries with moderate technological advancement but with highly awkward traffic science such as the Soviet Union. As most of these countries retained their traffic science awkwardness but at the same time collapsed in terms of technology and public finances, cheaper overground passages are getting more widespread there.
Subways may also be constructed for the benefit of wildlife.