Model Forum / General / Railroads / February 2010

Actually, track spacing is measured centre to centre; see excerpt from
http://en.wikipedia.org/wiki/Double_track below.

For model railways, the spacing has to be wide enough to prevent passing
trains from sideswiping each other. Space the tracks for the longest
rolling stock. In N it should be 1" or more centre to centre. You can
make a gauge for rail-to-rail spacing by laying down a couple of pieces
of track to the desired spacing, and cutting slots in a piece of 2mm
plastic to accommodate the inner rails. You may as well make one for
straight track and one (or more) for curved track. You can make four
gauges on piece of plastic, after all.

If you want prototypical accuracy, keep in mind that track spacing
varies by prototype, era, type of line, traffic, etc. IOW, if it looks
right, it is right.

HTH
wolf k.

Excerpt from Wiki article:

Track centres

The distance between the track centres makes a difference in cost and
performance of a double track line. The track centres can be as narrow
and as cheap as possible, but maintenance must be done on the side.
Signals for bi-directional working cannot be mounted between the tracks
so must be mounted on the 'wrong' side of the line or on expensive
signal bridges. Very narrow track centres are also undesirable for high
speeds, as pressure waves knock each other as high speed trains pass.

Narrow track centres might be 4 m or less. Narrow track centres may have
to be widened on sharp curves to allow for long rail vehicles following
the arc of the curve, and this increases a surveyor's workload. Widening
a track centre to 5 m or so suits high speed trains passing each other,
and eliminates the need to widen the centres on sharp curves. Increasing
width of track centres of 6 m or more makes it much easier to mount
signals and overhead wiring structures.

Very wide centres at major bridges can have military value. It also
makes it harder for rogue ships and barges knocking out both bridges in
the same accident.

The two relevant dimensions are "the four foot way" and the "six foot way".
The first is the gauge, which shows how wooley both those terms are.
Add the two together as they stand and you'd get a ten foot center to  
center
dimension between tracks, which would barely be workable. I'm sure the  
terms
originated back in the early years of railways when locomotives and rolling
stock were smaller and track spacing would have widened since.
The minimum spacing would allow two trains to pass with a man standing
between the tracks.
Of course once prototype double track has been laid and bridges, platforms,
crossovers etc  laid it would take an awful lot of work and materials to
relay them at a wider spacing,. With that in mind, the spacing on any given
piece of track is probably as laid in pre-grouping era. 12 or 13 feet would
probably be about right. Tracks laid for modern high speed trains would be
several feet wider.

On model curves the rolling stock swings at the outer corners and inside
center so tracks need wider spacing. The sharper the curves and the longer
the rolling stock, the further the swing will be so the wider the track
spacing required.
Generally steam locomotive models will extend further outside the curve
than Diseasals etc.

Nodel track spacing is a practical compromise that can't be avoided.
Narrowed gauge and increased spacing will always look wrong!

Greg.P.

On Feb 22, 1:08�am, Frank Erskine <frank.ersk...@btinternet.com>
wrote:

Others have given comprehensive replies but, as interesting aside, the
prototype 6ft can also be considerably smaller.  The tightest I ever
worked on as an engineer was the Maryport and Carlisle railway where,
at several overbridges, the 6ft came down to an actual 4ft 8ins!

For this reason, there was a 20mph speed restriction through those
bridges to reduce swaying and all units working that line had to have
bars on the opening windows.

George