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Traffic Flow, Density & Spacing Calculator

Relate average traffic counts, flow, density, spacing and speed.

  • Formula & worked example
  • Private in your browser
  • No signup
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Edit a calculated value to solve backwards, or lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

Sixty vehicles passing in 90 seconds give a flow of 2,400 vehicles per hour. Forty vehicles distributed over one kilometre give density of 40 per km, average spacing of 25 metres and implied speed of 60 km/h.

Flow = count ÷ observation time = density × speed; density = vehicles ÷ road length; average spacing = 1 ÷ density

Worked example

Enter these known values and leave the other values blank.

Vehicles passing the observation point
60
Observation duration
90 sec
Vehicles occupying the road segment
40
Road segment length
1 km
Traffic flow
2400 / hrs
Density
40 / km
Average spatial headway
25 m
Travel speed
60 km/h

Assumptions and limitations

  • No. It is average spatial headway in a traffic-flow model, not a driving recommendation. Use a consistent lane or road scope and distinguish a count passing one point from a count occupying a road segment.
  • Match the units shown and use measured inputs where available. The result follows the stated model and does not account for unentered changes.

Common questions

Is the spacing result a safe following distance?

No. It is average spatial headway in a traffic-flow model, not a driving recommendation. Use a consistent lane or road scope and distinguish a count passing one point from a count occupying a road segment.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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