OpenRoads Designer CONNECT Edition


Options: The spiral is defined as a length above. As an alternative, you may define the spiral by radius and one of the following by changing the method on the dialog.

  • Length - (Shown above) the length of the spiral

  • RL value - the spiral is defined by a parameter equal to the radius multiplied by length

  • A-Value - RL values can be quite large, so in some jurisdictions the A-value is used; A-value is equal to the square root of RL

  • Deflection - sometimes called spiral angle or theta angle; this is the deflection at the spiral point of intersection

  • Delta R - also called throw or spiral offset; this is the offset from the simple curve that would exist without a spiral to the same curve after a spiral is introduced


  • If base element is curved, the following applies:

If the spiral is constructed to the inside of the curve, then the beginning radius of the spiral will equal the radius of the base element instead of infinity and the spiral will be of same hand as the base curve.

If the spiral is constructed to the outside of the curve, then the start radius of the spiral will be infinity. This may not match all needs. It is common practice that a double spiral be constructed. The first spiral would be from curve radius to infinity and of same hand as base curve. The second spiral would be of opposite hand and go from infinite radius to the radius defined in the tool. This double spiral construct is not supported in this tool. Using multiple tools may produce a suitable construction.

  • Only clothoid spirals are supported by this tool.

Dialog Customization

Right-click on the dialog to customize it for specific tasks or user preference.


Manipulators are available for:

  • Offsets

  • Spiral Length


Arc Between Elements rule data is also accessible in the properties. The following properties are editable.

The following properties are read-only but can be useful for review.