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Calcimator

Turnout Design Calculator

Calculate railroad switch/turnout geometry from frog number — frog angle, lead length, curve radius, and maximum diverging speed.

Inputs

in

Results

Frog angle

5.73°

Turnout curve radius944 ft
Degree of curve6.07°
Lead length47.1 ft
Overall turnout length70.6 ft
Max diverging speed18.8 mph
Heel spread5.65 in
Closure rail length28.2 ft
Speed class1
How to Use This Calculator
  1. Enter Frog number (N) and Max unbalanced cant.
  2. Review the Frog angle (°) result.
  3. Use Turnout curve radius (ft) and Degree of curve (°) to inform your decision.

How the result changes with Frog number (N)

Frog number (N)Frog angle
6.68.67°
134.41°
212.73°
272.12°

What each input means

Frog number (N)
Turnout frog number (#6=yard, #10=branch, #15=main, #20=high-speed).
Max unbalanced cant
Maximum allowed cant deficiency through the turnout (typically 1.5 in).

What each result means

Frog angle
Angle of divergence at the frog point.
Turnout curve radius
Radius of the diverging route through the turnout.
Degree of curve
Equivalent degree of curvature.
Lead length
Distance from switch point to theoretical frog nose.
Overall turnout length
Approximate total length of the turnout assembly.
Max diverging speed
Maximum safe speed through the diverging route.
Heel spread
Spread between stock rail and switch rail at the heel block.
Closure rail length
Approximate length of the closure rail section.
Speed class
0=yard/low, 1=medium, 2=main line, 3=high-speed.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    Frog number (N) = 10, Max unbalanced cant = 1.5 = 2 input(s) provided
  2. Calculate Frog angle
    Frog angle = frogAngleRad * (180 / π)
    5.725 = 5.725
  3. Calculate Turnout curve radius
    944 = 944
  4. Calculate Degree of curve
    Degree of curve = 5729.578 / turnoutRadiusFt
    6.07 = 6.07

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