[Arnt]

Looks like the derivative of the angle is continuous.

When you drive around a street corner in a car, you start by turning the wheel to turn a little, then more, then less, then you drive straight again. This looks like that kind of curve.

[echoangle]

Some links on this with regards to roads/tracks:

https://en.wikipedia.org/wiki/Jerk_(physics)#In_the_geometri...

https://en.wikipedia.org/wiki/Track_transition_curve