AREA 10 Chord Spiral

Special note and disclaimer

The content of this web page is presented as historical information only.  It is hoped that this will be of some use to railroad historians, model railroaders, and math enthusiasts.  The Spiral Calculator Applet is run by the Java interpreter in your browser, therefore, the results are not guaranteed.  This is an unofficial site, and is not associated in any way with the American Railway Engineering Association (AREA).
 
Source

The information in these pages was obtained from AREA Committee V, Track, document published c. 1924.  Unfortunately, the only portion of the book was available was a copy of a few pages pertaining to track.  Some of the pages have footnotes referencing other AREA publications, with "Adopted" dates.  The latest "Adopted" date is 1924.

Contents

Notation  Graphically shows the AREA 10 Chord Spiral notation.
Formulas  Contains the AREA 10 Chord Spiral formulas.  These are the formulas that were used to implement the Spiral Calculator
Spiral Calculator Applet Spiral Calculator.  Please read the rest of this page before attempting to run the Calculator Applet.  The link is at the bottom of this page.
 

Feedback

Please send comments and questions to:  Dale Muir

Running the Spiral Calculator

Browser Requirements

The browser must support Java version 1.1 or better.

If you are using Internet Explorer, you must have Internet Explorer 4.1 or better. Internet Explorer 3.x will NOT run the calculator.

Microsoft Internet Explorer

If you are using Netscape, you must have Netscape 4.05 or better. The Spiral Calculator Applet will not run in Netscape 4.04.  If you get an error similar to "Verifier error CurveViewApplet.init()V: Cannot find class CurveView", you need to update Netscape.

Netscape

Known bugs

Internet Explorer 4.04 and Netscape 4.05 bugs

The browser's built in Java interpreter does not round values displayed properly.  Example:  A value of 99.999999 rounded to three decimal places should display as 100.000, but is displayed as 99.999.  In other words, IE 4.x truncates instead of rounding.  This does not affect internal calculations, only the displayed values.  The workaround is to round yourself.

Limitations

The spiral calculator currently does not have input checking.  The user is responsible for entering reasonable values until the next release.

The minimum radius is 100 feet, or a 60 degree curve.  This limitation is imposed by the AREA 10 Chord Spiral Formula.  Model railroaders: A scaled version is in the works.  For now, you will have to convert from real world dimensions to scale dimensions manually.

The AREA formula applies to spirals with a central angle ( Delta ) of 45 degrees or less.

Usage

  1. Choose Degree or Radius from the choice box.
  2. If you choose Degree, enter the Degree of Curve.  Value must be:  > 0 and <= 60.
  3. If you choose Radius, enter the curve radius in feet.  Value must be >= 100.
  4. Enter the spiral length in feet.  Value must be >= 0.
  5. Enter the number of spiral stations. (Number of points calculated.)  Reasonable values range from 1 to 20.  10 is the usual number.  Another common usage is to compute a station for every 1/2" change in super elevation.
  6. Enter the total central angle (angle between tangents) in degrees.  Value must be >= 2 * the central angle of the spiral ( Delta ) and <= 90.  This value is used only to compute Ts and Es, and does not affect the spiral itself.
Run Spiral Calculator Applet
 

More 10 Chord Spiral Information

  Notation  Formulas  Run Spiral Calculator Applet

More Railroad Information

 Railroad Home Page AREA Track Definitions Home