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Traffic Signal Timing Calculator

Work out traffic signal timing instantly with clear inputs, formula shown and shareable results.

About Traffic Signal Timing Calculator

Lost time is the amber plus all-red interval for every phase, and the effective green available is the cycle length less that lost time, divided between the phases. Lost time is fixed per phase, so a four phase junction on a short cycle can spend a third of every cycle with nobody moving, which is why cycle length and phase count are traded off.

Formulas

Lost time

lost = phases x (amber + all red clearance)

Green per phase

green = (cycle length - lost time) / phases

Worked example

With the default values below, Traffic Signal Timing Calculator returns Effective green per phase of 25.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Cycle lengthminimum 10 s
90 s
Number of phasesminimum 1
3
Amber time per phaseminimum 0 s
3 s
All red clearance per phaseminimum 0 s
2 s

Results

Effective green per phase
25.00 s
Time lost to amber and clearance
15.00 s
Cycles per hour
40.00
Approximate vehicles per hour per phase
500

Step by step

  1. 1Values used
  2. 2Lost time
  3. 3Green per phase
  4. 4Effective green per phase= 25.00 s
  5. 5Time lost to amber and clearance= 15.00 s
  6. 6Cycles per hour= 40.00
  7. 7Approximate vehicles per hour per phase= 500

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 Traffic Signal Timing figure worked out?

lost = phases x (amber + all red clearance). Lost time is the amber plus all-red interval for every phase, and the effective green available is the cycle length less that lost time, divided between the phases.

Why does this matter?

Lost time is fixed per phase, so a four phase junction on a short cycle can spend a third of every cycle with nobody moving, which is why cycle length and phase count are traded off.

What do I need to enter?

Enter cycle length, number of phases, amber time per phase, all red clearance per phase. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.

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