Signal Spacing Calculator

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

About Signal Spacing Calculator

A block section must be long enough that a driver seeing a caution aspect can stop before the next signal: braking distance plus sighting distance plus the overlap beyond the signal, with a safety margin. That length then sets the minimum achievable headway on the line.

Formula

Signal spacing

spacing = (braking distance + sighting distance + overlap) x (1 + margin)

Worked example

With the default values below, Signal Spacing Calculator returns Minimum signal spacing of 1,408. Change any input above and every figure here is recalculated in your browser.

Inputs used

Service braking distance: 900 m
Sighting distance: 200 m
Overlap beyond the signal: 180 m
Safety margin: 10 %

Results

Minimum signal spacing: 1,408 m
Block section length: 1,280 m
Margin included: 128 m
Headway implied at 80 km/h: 127 s

Step by step

1Values used
2Signal spacing
3Minimum signal spacing= 1,408 m
4Block section length= 1,280 m
5Margin included= 128 m
6Headway implied at 80 km/h= 127 s

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 whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Rail results are planning estimates only. Verify against the infrastructure manager's rule book, approved braking curves and applicable railway safety regulations.

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

Rail results are planning estimates only. Verify against the infrastructure manager's rule book, approved braking curves and applicable railway safety regulations.

Frequently Asked Questions

Why include an overlap?

It protects against a slight overrun past a red signal, keeping the conflict point clear. Typical overlaps are 180-200 m.

How does spacing affect capacity?

Shorter blocks allow closer following and higher capacity, which is why resignalling with more, shorter blocks or moving-block ETCS Level 3 increases throughput.