# Double track geometry

What is the actual "six foot" spacing between double track lines, and is it measured between the inner faces of each track i.e. at the wheel
flange point, or the outer edge of each track?
I'm sure I had a proper drawing of this somewhere, but can't put my hands on it at the mo... :-(
I have an idea that in such as N scale, this is increased a bit - if so, by how much?
TIA...
--
Frank Erskine
Sunderland
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Frank Erskine wrote:

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.
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wrote:

Many thanks -
--
Frank Erskine

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But not when referring to "the 6 foot" which is measured rail to rail.
Whether it's inner or outer face of the rail is largely immaterial, an inch or two in seventy-two.
The "6 foot" varied so shouldn't be taken as an absolute.
How much you need to increrase the spacing of model track (any gauge or scale) depends on how tight your curves are.
MBQ
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snipped-for-privacy@hotmail.com wrote:

True, if you're referring to the ganger's gauges. But the tracks are surveyed and laid out along centre lines.
[...] wolf k.
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On Mon, 22 Feb 2010 14:08:56 +1300, Frank Erskine

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.
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No - the six foot is exactly that. Standard double track spacing on straights is 11' 2" : 4' 8.5" plus twice the rail thickness (nominal 2.75") plus six feet. Source: Ministry of Transport Requirements - 1950 edition. The only historic routes where there has been any substantial increase on this are ex-broad gauge, where the spacing between platforms opens out by an extra 4' 7".
You are right that modern high speed lines have a wider spacing.
Stuart J
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On Tue, 23 Feb 2010 14:48:36 -0800 (PST), StuartJ

Many thanks to all for their very helpful comments. It seems that there's scope (and sometimes necessity!) for a measure (!) of modeller's licence, especially on tight bends, but it's also nice to know what the 'official' dimensions are.
Regards -
--
Frank Erskine
Sunderland
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wrote:

As a matter of interest were things different on the GWR with the reduction of guage from broad to standard. Did they use any of the extra space between tracks or on one or both sides. Did they reduce the total width immediately or over time ?
Then theres the Great Central, wasnt that different as it was built to continental loading guage ?
Cheers, Simon