Track spacing

The distance between the track centres makes a difference in cost and performance of a double-track line.

In fact, the first Prussian railways were built to that standard but it soon became apparent that it was too dangerous with some passengers having a hand or their head out of the window.

Increasing width of track centres of 6 m (20 ft) or more makes it much easier to mount signals and overhead wiring structures.

With the trains going faster over time, the track centres were increased to 4 m (13 ft) on main lines.

The first update of 1982 increased the minimum track centre to 4 m (13 ft) allowing no more exceptions.

But by 1991 it was replaced with a table taking into account the maximum speed of the trains on a track as well as the curvature.

Additionally, these lines are only allowed for high-speed passenger rail where no out-of-gauge loads are expected and the windows in the trains can not be opened.

[1] The largest minimum track centre is planned for Indias high-speed network requiring a common distance of 5.3 m (17 ft).

For an actual construction the distance is measured from the inside of a rail head to the matching one of the other track.