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Spiral Curve Data

This document shows the way that spiral curve data should be shown on Highway Design plans and briefly describes the meaning of each item listed.

Sample Curve Data

Follow the link to a graphic depicting the variables related to spiral curves.


sample curve data

Detail in leading spiral curve area.

Spiral Curve Data
Abbreviation Example Description
PI PI= 23+96.20 Station of intersection point of start and end tangents
N N = 405083.92 North coordinate
E E = 964724.93 East coordinate
Δ Δ = 77°-47'-44.8" RT Angle between start and end tangents
Δc Δc = 39°-35'-54.9" RT Angle turned by the circular portion of the curve
Dc Dc = 19°-05'-54.9" Degree of curve on Imperial alignments
Ts Ts = 346.15' Distance from tangent point to intersection of tangents
Es Es = 92.58' Distance from PI point to curve
Ls Ls = 200.00' Length of spiral
Lc Lc = 207.34' Length of circular portion of curve
Rc Rc = 30 0.00' Radius of circular curve
LT LT = 134.12' 'Long Tangent' of spiral curve
ST ST = 67.38' 'Short Tangent' of spiral curve
θs θs = 19°-05'-54.9" Angle turned by spiral portion of curve
P P = 5.53' Offset of circular curve from tangent line at the point where the circular curve would be parallel to the tangent if it were extended.
K K = 99.63' Distance along the tangent to the point described immediately above (marginally less than half the length of the spiral)
Xc Xc = 197.79' Distance along tangent from point of tangency to end of circular curve
Yc Yc = 22.05' Distance perpendicular to tangent from tangent line to end of circular curve
LC LC = 199.01' 'Long Chord' distance between ends of the spiral

New Hampshire Department of Transportation
PO Box 483  |  7 Hazen Drive  |  
Concord, NH  |  03302-0483
Tel: 603.271.3734  |  Fax: 603.271.3914