Track transition curve: Difference between revisions

Revision as of 11:12, 19 January 2015

Revision as of 15:39, 17 February 2015

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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:CornuSprialAnimation.gif|thumb|Animation depicting evolution of a Cornu spiral with the tangential circle with the same radius of curvature as its tip (click on linkthumbnail to observe and then select `View original file' at bottom right).]]

[[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]], where a straight section changes into a curve. It is designed to prevent sudden changes in [[centripetal acceleration|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 [[Cant (road/rail)|bank]] is reached.