> The first thing that springs to mind is how amazing smooth the rails were in the V150 test.
High speed lines are necessarily extremely smooth and with very small tolerances.
French lines come out the factory in rail pieces 200 to 400 meters long and are thermite-welded together after adjustment. They have no expansion joints except around bridges (and even then not necessarily)
So how do they handle thermal expansion? Just let the whole system build up huge pressures in the summer? Special alloys that don't expand so much in the heat?
I learned recently that rail (especially continuously welded rail) is generally kept under tension (I don't understand how it is secured at the end of the line, though). So when it heats up in the summer, it is simply under less tension.
Unless it heats up too much, and then it buckles and you get derailments.
> Just let the whole system build up huge pressures in the summer?
Pretty much yes, that's why the rails have to be adjusted very precisely, otherwise they're going to kink / bend in summer (if pressure gets too high) and crack in winter.
High speed lines are necessarily extremely smooth and with very small tolerances.
French lines come out the factory in rail pieces 200 to 400 meters long and are thermite-welded together after adjustment. They have no expansion joints except around bridges (and even then not necessarily)