In the US and other American countries, interstate highways are often inaccessible for pedestrians and to facilitate their movement, underpasses are made. In general, a depressed roadway underneath a main passage is called an underpass. In fact, subway is the term used to refer to passages made underneath a railway or a highway. They are more commonly seen in England and other commonwealth countries than North America. Underground passages are more common and older than flyovers as in earlier times they were made under an existing road to allow for safe passage of pedestrians. Flyovers or overpasses are engineering marvels and at places, they make a crisscross of roads over a main road that not only looks beautiful, but allows for faster and more efficient transport of people and vehicles.

In such situations, a flyover is exactly like an underground tunnel (like an underground subway) only that it is built in air and is open. Sometimes, a flyover is made only for pedestrians to allow for their safe passage over a busy main road. At times, it looks like a bridge across a road, and at times, a flyover gives the appearance of a road flying over another road. Sometimes, a flyover is a railway passage made over an underneath railway passage. In general a flyover is an overpass that is constructed over a main road to facilitate movement of people or railway. Though both flyovers and underpasses serve the same purpose of making transport easier, there are many differences between them arising mainly because of differences in design and architecture. They become a necessity when roads are congested because of heavy traffic and people of one locality find it difficult to move to another having to take diversions instead of getting a straight road that would save a lot of time and effort. Flyovers and underpasses are two important constructions that allow for more efficient and faster transport.

Underpass tunnel