A railway is a system of systems: track, structures, overhead power, signalling, telecoms and drainage, all working within millimetres along hundreds of kilometres, and all built while trains keep running nearby. Here is what a BIM coordinator needs to know to work on one.
Railways look simple from the platform: two rails and some wires. Behind that sits one of the most tightly integrated pieces of infrastructure there is, with millimetre tolerances over hundreds of kilometres, several disciplines sharing a narrow corridor, and a live railway next to the work.
Rail alignments have everything a road alignment has (straights, curves, transitions, grades, vertical curves) plus cant: the outer rail raised on curves. Cant changes gradually along transitions, and the rate of change is limited. Standard gauge, the distance between the rails, is 1,435 mm on most of the world's main lines.
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