Talk:Dual gauge

Error in picture - the 1435mm gauge is probably 1067mm gauge, as on Sakhalin Island. The difference between 1520 and 1435 is only 85mm which is actually very small. Label "1435mm" should be "1067mm". ^[1]

Hi, I understand that rail gauges must be a certain distance apart to allow a three-rail arrangement, while close gauges require four rails. However, what is the limit between the two? i.e. what is the minimum distance between gauges that allows for three rails? It's surprisingly difficult to look up this information. It seems to be somewhere around 6 inches or so, but I'm not sure. And is this different for narrow vs broad gauges? I read somewhere that 3 ft (914 mm) & 3 ft 6 in (1,067 mm) can fit on three rails, while ~5 ft (1,520 mm) and 5 ft 6 in (1,676 mm) cannot, despite them both being ~6 in apart. Is this correct, or off-base? More info would be appreciated. Xcalibur (talk) 20:55, 19 October 2022 (UTC)

Hello Xcalibur, the limiting factors are (1) the width of the bases of flat-bottom rails (the lighter the rail, the smaller the dimension), and (2) the method of fixing the rails to the baseplate/sleeper/tie. If you look at this photo that I took, which shows rails for 1435 mm (4 ft 8+1⁄2 in) and 1600 mm (5 ft 3 in) gauges, you'll see that a special sleeper/tie plate is used, which incorporates a ridge holding the two rail bases at minimum-possible distance. There is provision for spikes in this gap; without those holes it would be very difficult indeed to have the rails as close as this.

Taking the ASCE standard for 60 pounds/yard flat-bottom rail, the base is 4.25 in (108 mm) wide and the head is 2.375 in (60 mm). The ridge in the baseplate in the photograph is 1.5 inches (38 mm) wide. The gap between the rail-heads is therefore (base – head) + gap at base = 4.25 – 2.38 + 1.5 = 3.38 ins or 86 mm.

So my answers are:

• 3.38 ins or 86 mm is the practical minimum gap at the rail-head for 60 pound rails.
• This gap applies when two gauges are different by 165 mm (6.5 in), i.e. 1600 mm (5 ft 3 in) and 1435 mm (4 ft 8+1⁄2 in). The gauge pairs you mention -- 3 ft (914 mm) & 3 ft 6 in (1067 mm) and ~5 ft (1,520 mm) and 5 ft 6 in (1676 mm) -- are different by 153 mm (6.0 in) and 156 mm (6.1 in) respectively. These are less than the workable example I've described, so to my mind they wouldn't be possible to construct.

Cheers, Simon – SCHolar44 🇦🇺 💬 at 10:22, 21 October 2022 (UTC)

Exactly the answer I was looking for, thanks for this! That really clarifies the topic in a scholarly/professional manner. Yes, 6.5 in seems to be correct, and it fits with the observation that Standard & Irish gauge can fit on three rails, but just barely. The claims I've seen about combining those other gauge pairs with a third rail were therefore mistaken. Hopefully you understand why that led to confusion. Now that it's cleared up, I'll remove the inaccurate information from the article. Appreciate the input! Xcalibur (talk) 19:23, 22 October 2022 (UTC)

Under "Dual gauge (three rails)" I don't understand why, if the difference between gauges is small, a separate set of inner rails can be fit even though it's stated that isn't room physically to install just a single inner rail — which would be farther from the nearest outer rail than in the 4-rail construction.Casey (talk) 17:37, 30 March 2023 (UTC)

Hello Casey, Try as I may, I can't understand your question. Could you elaborate a bit more? Cheers, Simon – SCHolar44 🇦🇺 💬 at 21:37, 30 March 2023 (UTC)

Tnx for the query. Visualize initially that only a "broad" gauge line with 1435-mm spacing is there. Then, say a "narrow" gauge line of 1000-mm spacing is to be installed. If a 3-track scheme is used, the spacing between the close rails will be 1435 minus 1000 plus width of new 3rd railhead. But on 4-track scheme, the spacing on both sides is 1435/2 minus (1000/2+2*railhead width) — and the spacing at the foot of the rails will be less also. In practice, the decision may depend on what apparatus (tie plate, spike or screw) is used to secure all this to the tie, and even more so on the widths of the foot of the rail segments. Also, I suppose, on whether the outer track is already there with a new narrow-gauge capability to be installed later vs starting from scratch with new paraphernalia for everything. An unrelated thought is that with 3 rails all must be the same height, whereas with 4 rails the two inner rails could be slightly shorter.Casey (talk) 01:05, 2 April 2023 (UTC)

Aha! Got it, Casey!

For reasons of cost (including that of turnouts – three-rail configurations are less complex), 3-rail dual-gauge track is always the first preference. Only when the difference between the two gauges is less than somewhere in the range 145 millimetres (5.7 inches) to 200 millimetres (7.9 inches) (depending, as you say, on the tie plate, spike, screw – or clip – and the rail size) will 4 rails need to be resorted to.

When 4-rail dual-gauge is installed, the space constraints are removed (in a marshalling yard, the rails may even fit on a pre-existing tie). The photo in the 4-rail gallery of four-rail dual-gauge track (1520 and 1435 mm / ~5 ft and standard gauge) in Lithuania is an example of new track where purpose-made ties have been laid (see the old timber ties stacked on the far right too).

Differences in rail height/weight could be incorporated into plain dual-gauge track, especially in yards (at most the height difference would be 20 mm), but because of the complexities of incorporating two sizes at turnouts there needs to be a transition from the smaller rails to larger before the turnout is reached. In practice it is usually simpler to install the third/fourth rail(s) in dual-gauge track the same weight. The gallery photo of the standard-gauge cattle car on 4-rail triple-gauge track is an example.

With the widespread change to automated track-laying with concrete sleepers and rail clips, I expect upgrading most future mixed-gauge track will be on the basis of "pull everything out, start again".

My 2 cents' worth. Hope this answers your questions. If not, please get back.  :-) Cheers, Simon – SCHolar44 🇦🇺 💬 at 06:06, 2 April 2023 (UTC)

@Casey56: IIUC, when 4-rail track is used because there wouldn't be room between the two "separate" rails of 3-rail track (as opposed to the "common" rail), the 4 rails are not laid on a common axis of symmetry (ABBA) but somewhat out-of-axis (ABAB). If I'm mistaken, someone please correct me. — Tonymec (talk) 10:03, 10 April 2023 (UTC)

I have undertaken a major re-write of the article, excluding the Dual gauge by nation section. First, because it had been littered for a long time with unreferenced text, much of it of limited value or poorly expressed, leaving an impression of lack of focus and disjointedness. (The Dual gauge by nation section has similar faults, but at 2500 words long with only four references, it's beyond my capacity to rectify.) The text I deleted included some with significant errors.

The article had 36 photos when Trainsandotherthings reduced them to 18 on 30 August, saying "This article already has MORE THAN ENOUGH photos." I fully agree with that remark. I looked through the remaining images and their captions, and concluded that the range of track configurations could still be improved by adding some new photos and deleting some of the remaining ones. The total now is 14 in three galleries plus three others. I may compile a small gallery for the Alternatives to dual-gauge track section.

I formatted the galleries without using "gallery" coding so that the photos would be accessible on mobile devices – hence making them only 2 images wide.

I saved display space by setting the following to "collapsed":

• the galleries
• the Occurrences of triple gauge table.

I replaced the very long Track gauge sidebar with a text box containing a link to the sidebar in the Gauge article, to avoid WP:STACKING and because it isn't of great importance in this (dual gauge) article. Similarly, I have taken the long list of countries out of the table of contents.

With the text, my aim was to demonstrate factually what forms of multiple gauges exist, why, what the main constraints are, and what the alternatives to dual-gauge track are. It was a huge challenge digging out references for these subjects, but I eventually achieved coverage, albeit to a large extent through Australian sources. This was because (a) I have / have access mainly to them, (b) the whole subject is sparsely covered in the literature to the technical depth required here. Anyone desiring wider-scope documentation is very welcome to add (referenced) text.  ;-)

Feel free to discuss here, especially if you would like to find why I have made a particular decision. Cheers, Simon – SCHolar44 🇦🇺 💬 at 03:45, 8 November 2022 (UTC)

Update: I have removed or moved around a small number of photos and added some others to give a better coverage (and to correct some that I had put in the wrong gallery). I also added a small gallery showing centralisers and common-rail change-over devices. The new ones are due to a friend to whom I casually mentioned the photos I needed, who replied "I took a heap of photos at Gladstone in the early 1970s". It's good to have friends! :-) Cheers, Simon – SCHolar44 🇦🇺 💬 at 08:32, 29 November 2022 (UTC)