iPhoneOgraphy – 20 Apr 2016 (Day 111/366)
An overpass (called a flyover in the United Kingdom and some other Commonwealth countries) is a bridge, road, railway or similar structure that crosses over another road or railway. An overpass and underpass together form a grade separation. Stack interchanges are made up of many overpasses.
The world’s first railroad flyover was constructed in 1843 by the London and Croydon Railway at Norwood Junction railway station to carry its atmospheric railway vehicles over the Brighton Main Line.
Railway overpasses are used to replace level crossings (at-grade crossings) as a safer alternative. Using overpasses allows for unobstructed rail traffic to flow without conflicting with vehicular and pedestrian traffic. Rapid transit systems use complete grade separation of their rights of way to avoid traffic interference with frequent and reliable service.
Railroads also use balloon loops and flying junctions instead of flat junctions, as a way to reverse direction and to avoid trains conflicting with those on other tracks.