The rails used in rail transport are produced in sections of fixed length. Rail lengths are made as long as possible, as the joints between rails are a source of weakness. Throughout the history of rail production, lengths have increased as manufacturing processes have improved.
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Timeline
The following are lengths of single sections produced by steel mills, without any thermite welding. Shorter rails may be welded with flashbutt welding, but the following rail lengths are unwelded.
Welding of rails into longer lengths was first introduced around 1893, making train rides quieter and safer.
Modern production techniques allowed the production of longer unwelded segments.
Multiples
Newer longer rails tend to be made as simple multiples of older shorter rails, so that old rails can be replaced without cutting. Some cutting would be needed as slightly longer rails are needed on the outside of sharp curves compared to the rails on the inside.
Boltholes
Rails can be supplied pre-drilled with boltholes for fishplates or without where they will be welded into place.
There are usually 2 boltholes or 3 boltholes.