Grade Separation - Railways

Railways

Attempts have been made to increase the capacity of railways by making tracks cross in a grade-separated manner, as opposed to the traditional use of flat crossings to change tracks. A grade-separated rail interchange is known as a flying junction and one which is not a level junction.

In 1897, the London and South Western Railway (LSWR) made use of a flying junction at Worting Junction south of Basingstoke to allow traffic on the Salisbury and Southampton routes to converge without conflicting movements; this became known as "Battledown Flyover". Also in Britain, the Southern Railway later made extensive use of flying junctions on other parts of its busy former LSWR main line.

Today in Britain, the tightly grouped nest of flying junctions to the north of Clapham Junction railway station—although technically a combination of many junctions—handle more than 4,000 trains per day (about one train every 15 seconds).

In the French TGV system, all high-speed junctions are grade-separated. The three fully grade-separated high-speed triangles on the LGV system are capable of being taken at speeds between 160 km/h–320 km/h (100 mph–200 mph).

In the United States, a flying junction on the Nickel Plate Road through Cleveland, Ohio, United States was completed in 1910. 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.

In railway construction, grade separation also means the avoidance of level crossings by making any roads crossing the line either pass under or over the railway on bridges. This greatly improves safety and is crucial to the safe operation of high-speed lines. The London Extension of the Great Central Railway, built between 1896 and 1899, was the first fully grade-separated railway of this type in the UK.