A track transition curve, or spiral easement, is a mathematically calculated curve on a section of highway, or railroad track, where a straight section changes into a curve. It is designed to prevent sudden changes in lateral (or centripetal) acceleration. In plan (i.e., viewed from above) the start of the transition of the horizontal curve is at infinite radius and at the end of the transition it has the same radius as the curve itself, thus forming a very broad spiral. At the same time, in the vertical plane, the outside of the curve is gradually raised until the correct degree of bank is reached.
If such easement were not applied, the lateral acceleration of a rail vehicle would change abruptly at one point – the tangent point where the straight track meets the curve – with undesirable results. With a road vehicle the driver naturally applies the steering alteration in a gradual manner and the curve is designed to permit this, using the same principle.
Famous quotes containing the words track, transition and/or curve:
“The world leaves no track in space, and the greatest action of man no mark in the vast idea.”
—Ralph Waldo Emerson (1803–1882)
“Some of the taverns on this road, which were particularly dirty, were plainly in a transition state from the camp to the house.”
—Henry David Thoreau (1817–1862)
“The years-heired feature that can
In curve and voice and eye
Despise the human span
Of durance—that is I;
The eternal thing in man,
That heeds no call to die.”
—Thomas Hardy (1840–1928)