You can basically use them for anything. But: they will still help drain battery power sooner and will still sound louder than the other pieces of track.
Do you still have them in your layouts?
Measured, a straight track is exactly 12.75 cm in length, and so is a curved track in the very middle.
The diameter of the outer circle, as lying down on my floor - that is, neither tensed nor expanded -, is 70.5 cm.