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Comment by iggldiggl | Hacker News Reader

But they are set into prefabricated concrete sleepers, which cannot be modified to a new track gauge and instead need to be swapped out completely. Whereas during the US gauge change, the railways used wooden sleepers, with the rails fastened simply with nails hammered into the sleepers, so it was simply a matter of pulling out the nails and hammering them in again at the new track gauge.

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There are machines these days that change sleepers automatically. I do not know if they do gauge conversion, but changing track (meaning replacing old one) and sleepers nowadays is fully automated.

I imagine running a machine in reverse, removing the track and changing sleepers and one moving forward at the same time installing the new track only. Or have one remove the old sleepers and track and and another one installing new sleepers and track (imagine building new track kind of operation).

Yes, those kind of track relaying machines exist, and they could most likely be adapted to work for the gauge change (one end of the machine would have to be set up for broad gauge and the other end for standard gauge), but they still manage only a few kilometres of track per day, and they're comparatively rare and expensive – basically there are only enough of them around for the amount of track relaying required during routine maintenance.

So repeats of the famous 19th century gauge change by converting large swathes of the network in just a few days (thousands of miles of track as in the US in 1886, or even just the 177 miles west of Exeter in the UK in 1892) remain rather unlikely.

There are metal sleepers that sit on a concrete pad. The challenging part is the rail is encased in concrete that enables drivers to drive over the tracks.

Getting to the sleepers would take weeks of jackhammering plus more time to repour the concrete.

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