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

Detail in leading spiral curve area.

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 |

Î¸s | Î¸s = 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