are used to describe train directions on railroad systems. The terms used may be derived from such sources as compass directions, altitude directions, or other directions. However, the railroad directions frequently vary from the actual directions, so that, for example, a "northbound" train may really be headed west, or a train going "down" may actually be increasing its elevation. Directions are often specific to system, country, or region.
In France, railway directions are usually described as Impair
, meaning Odd
and corresponding Down
in British system. Impair
means leave from Paris and Pair
means towards Paris. This convention extends to not only the trains and the tracks, but also to lineside equipments.Pair
is also homophonic with Paris
, so direction P is equivalent either with direction Pair or with direction Paris.
In China, railway directions are described as "up" (上行) and "down" (下行), with up towards Beijing
; trains leaving Beijing are "down", while those going toward Beijing are "up". For railways not connected with Beijing, north and west are used as "up" and east and south as "down". Odd numbered train codes are used for "down" trains, while even numbers are used for "up"; for example, train T27 from Beijing west
is "down" (going away from Beijing) since 27 is odd.
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