Relative routing

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Relative alignment with the help of the radius tulip

The Relationstrassierung is a planning principle in the design of fast traffic roads. Radii of successive curves are chosen so that they are in a harmonic relationship to one another. In this way, traffic safety is increased, since the vehicle driver does not drive through an abrupt change in the curvature in successive curves. Depending on the road category, the guidelines for the alignment of roads specify how much the radii of successive curves should at most deviate from one another.

For example, the RAS-L previously valid in Germany contain the so-called radius tulip , which represents the connection between two successive radii. For road categories AI and A II, the selected radius sequence should be in the “good range”, for road categories A III and A IV in the “usable range”. Any further radius sequences should be avoided. If constraints such as topographical or structural conditions do not allow relative alignment, appropriate measures such as the use of guidance systems or speed limits must be taken.


  • Günter Wolf: Road planning . Werner Verlag, Munich 2005, ISBN 3-8041-5003-9 , pp. 107 ff .