Track transition curve: Difference between revisions

Revision as of 20:34, 7 June 2020

Revision as of 20:39, 7 June 2020

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[[Image:Easement curve.svg|240px|thumb|The red [[Euler spiral]] is an example of an easement curve between a blue straight line and a circular arc, shown in green.]]

[[File:CornuSpiralAnimation.gif|thumb|Animation depicting evolution of a [[Cornu spiral]] with the tangential circle with the same radius of curvature as at its tip, also known as an [[osculating circle]] (click on thumbnail to observe).]]

[[Image:Parabolic transition curve.JPG|thumb|240px|This sign aside a railroad (between [[Ghent]] and [[Bruges]]) indicates the start of the transition curve. A [[parabolic curve]] (''POB'') is used.]]

A '''track transition curve''', or '''spiral easement''', is a mathematically-calculated curve on a section of highway, or [[track (rail transport)|railroad track]], in which a straight section changes into a curve. It is designed to prevent sudden changes in [[centripetal acceleration|lateral (or centripetal) acceleration]]. In plane (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 and so forms 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 [[cant (road/rail)|bank]] is reached.