train every 15 seconds). Virtually all major railway lines no longer cross (forming an 'X' shape) at flat level (although many diverge - i.e. 'Y' shape). High-speed railways (+) On almost all high-speed railway lines, the faster speed requires grade separation. Therefore, many high speed lines are elevated, especially in Taiwan and Japan, where population density alongside high speed lines is higher than in France, Italy or Germany. In the United States, a flying junction on the Nickel Plate Road through Cleveland, Ohio, United States was completed in 1913. The most frequent use was later found on the former Pennsylvania Railroad main lines. The lines are included as part of the Northeast Corridor and Keystone Corridor now owned by Amtrak. The most complex of these junctions, near Philadelphia Zoo, handles railway traffic for Amtrak, SEPTA, New Jersey Transit, Norfolk Southern, CSX Transportation, and Conrail. In what is known as "area 1520", which includes the former Soviet Union and other regions using the same gauge, the most complicated grade-separation railpoint is found at Liubotyn in Ukraine. Footbridges and subways Footbridges and pedestrian/cyclist subways (called underpasses in North America as well as in the United Kingdom when referring to roads) are often employed to allow pedestrians and cyclists to cross busy streets and highways. Though introduced to Central Park in New York City in the 1860s, subways are far more common today in Europe, especially in countries such as the Netherlands, and Denmark where cycling is strongly encouraged. Long underpasses may be called tunnels. References Junction types