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Green Time Split Calculator

Work out green time split instantly with clear inputs, formula shown and shareable results.

About Green Time Split Calculator

Green time is allocated in proportion to each phase's critical flow ratio, so every approach ends up with the same degree of saturation. Total effective green is the cycle length less lost time, and splitting it by the ratio of the flow ratios equalises delay rather than equalising green.

Formula

Green split

gi = (cycle - lost time) x yi / sum of all yi

Worked example

With the default values below, Green Time Split Calculator returns Effective green for phase one of 42.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Cycle lengthminimum 20 s
90 s
Total lost timeminimum 1 s
12 s
Critical flow ratio for phase oneaccepts 0.01–0.95
0.35
Critical flow ratio for phase twoaccepts 0.01–0.95
0.3

Results

Effective green for phase one
42.0 s
Effective green for phase two
36.0 s
Total effective green
78.0 s
Phase one share of green
53.85% %

Step by step

  1. 1Values used
  2. 2Green split
  3. 3Effective green for phase one= 42.0 s
  4. 4Effective green for phase two= 36.0 s
  5. 5Total effective green= 78.0 s
  6. 6Phase one share of green= 53.85 %

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Green Time Split figure worked out?

gi = (cycle - lost time) x yi / sum of all yi. Green time is allocated in proportion to each phase's critical flow ratio, so every approach ends up with the same degree of saturation.

Why not give equal green to each phase?

Because approaches carry different flows. Equal green over-serves the light approach and starves the heavy one, producing far more total delay than a proportional split.

What values do I need to enter?

This calculator takes 4 inputs: Cycle length, Total lost time, Critical flow ratio for phase one, Critical flow ratio for phase two. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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