Transition Spiral Curves Transition curves are curves of variable radius placed

# Transition spiral curves transition curves are curves

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Transition (Spiral) Curves Transition curves are curves of variable radius placed between straights and circular curves or between two circular curves of significantly different radii for the following reasons: For easy steering operation and riding comfort. The use of transition curves provides a vehicle path that gradually increases or decreases the radial force as the vehicle enters or leaves a circular curve. The degree of a transition curve placed between a tangent and circular curve varies from zero at the tangent end to the degree of the circular curve at the curve end. To provide lengths over which superelevation and widening can be applied To improve the appearance of the road by removing sharp discontinuities in alignment at the start and end of circular curves The minimum length of a transition curve is a function of the design speed, the rate of gain of radial acceleration and the radius of the circular curve as follows: where, Ls= minimum length of transition, V= design speed (kph), R= radius of circular curve C= rate of gain of radial acceleration (0.3572 m/sec.sq) 3 3 3 0.06 3.6 s V V L R CR
Lecture 5 13/04/14 9 Design of Horizontal Alignment The Shift Criterion: The minimum length of transition can also be determined using the “shift method”. The shift is the offset of the start of the circular curve from the line of the tangent. Sketch: The minimum limit of the shift recommended is 0.2m. For values below 0.2m, transition curves are deemed not necessary. The shift is computed as: Where, S= shift (m), Ls= transition length (m); R= radius of circular curve (m) 24 s L S R

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• Osculating circle

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