Transition Curves
A curve should not become a straight all at once, but should gradually increase in radius over time (a distance of around 40 m - 80 m for a line with a maximum speed of about 100 km/h). Even worse than curves with no transition are reverse curves with no intervening straight.
The super-elevation (aka cant) must also be transitioned.
The higher the speed, the longer the transition.
Read more about this topic: Minimum Railway Curve Radius
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