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Dual gauge track has three or four rails, so that trains of two different track gauges can run on the same line. Railways use it where a narrow-gauge line meets a standard-gauge one, or during a change of gauge; modellers love it because few things look as intriguing as a narrow-gauge train and a standard-gauge one sharing the same sleepers.
A railway’s gauge is the distance between the inside faces of its two rails. “A dual gauge railroad track has three or four rails, allowing vehicles of two track gauges to run on it” (Wikipedia, Dual gauge). The commonest case is a narrow gauge, such as 3 feet (914 mm) or metre gauge (1,000 mm), sharing track with standard gauge (1,435 mm, 4 ft 8½ in).
Dual gauge track is sometimes called mixed gauge. It is not the same as a break of gauge, where two gauges meet end to end and goods must be moved from one train to another, and it is not the same as variable-gauge wheelsets, which change the train instead of the track.
Most dual gauge track has three rails. One rail, the common rail, is used by both gauges; a second rail gives the narrow gauge and a third the wider gauge. It is cheaper than four rails, but the common rail wears faster than the others, and trains of the two gauges run off-centre from each other, which matters at platforms and in tunnels (Wikipedia).
Three rails only work when the two gauges are far enough apart for the rails and their fastenings to fit between them: the rails must be at least about 40 mm (1.6 in) apart at the base (Wikipedia).
When the two gauges are too close for a third rail, for example metre gauge (1,000 mm) and Cape gauge (1,067 mm) in Africa, or standard gauge (1,435 mm) and Russian-type broad gauge (1,520 or 1,524 mm), four rails are needed. Four rails are also used where both gauges must stay on the same centre line, in tunnels, on bridges and on turntables (Wikipedia).
Where four-rail track is laid only through a narrow spot and the lines then separate again as soon as there is room, it is called gauntlet track (gantlet in the US) (Wikipedia).
Plain dual gauge track is simple. The points are where it gets interesting. Wherever a rail of one gauge has to cross a rail of the other, there must be a crossing (frog) with flangeways, so a dual gauge turnout has more crossings, more check rails and more moving parts than a plain one.
The tolerances are tight. Wikipedia notes that dual gauge turnouts must be held to only 8 mm (0.31 in) over gauge and 2 mm (0.079 in) under. Signalling is harder too, because track circuits and interlocking must work for both gauges at once, and a mistake can send a train onto rails of the wrong gauge: in 2004 a Czech express derailed after a signalling error routed a standard-gauge train onto narrow-gauge track (Wikipedia).
| Where | Gauges | Notes |
|---|---|---|
| Denver to Golden, Colorado, USA | 3 ft and standard | Colorado & Southern; dual gauge until 1941 |
| Alamosa to Antonito, Colorado, USA | 3 ft and standard | Denver & Rio Grande Western; dual gauge until the 1960s |
| Mount Union, Pennsylvania, USA | 3 ft and standard | East Broad Top Railroad yard |
| Didcot, England | 7 ft ¼ in broad and standard | Short section preserved by the Great Western Society |
| Fairbourne Railway, Wales | 15 in and 12¼ in | Laid in the late 2010s for visiting trains at special events |
| Baie de Somme, France | Metre and standard, four rails | Noyelles-sur-Mer to Saint-Valery-sur-Somme |
| Lucerne to Horw, Switzerland | Metre and standard | Zentralbahn: narrow-gauge passenger trains, standard-gauge freight |
| Chur to Domat/Ems, Switzerland | Metre and standard | Rhaetian Railway |
| Seikan Tunnel approach, Japan | Cape gauge and standard | 82.1 km (51.0 mi), the longest dual gauge section in Japan |
| Zaragoza to Huesca, Spain | Iberian and standard | 21.7 km (13.5 mi), for high-speed and conventional trains |
| Victoria, Australia | 5 ft 3 in broad and standard | Several sections around Melbourne and Geelong |
| Haparanda to Tornio, Sweden and Finland | Standard and 1,524 mm, four rails | About 2 km across the border bridges |
All entries from Wikipedia, Dual gauge, read 14 October 2026, which lists many more. A few places even have triple gauge: Barcelona, for example, has track for metre, standard and Iberian gauge.
In a model, the narrow gauge almost always runs on the track of a smaller scale: HOn3 trains on 10.5 mm track beside HO trains on 16.5 mm, for example. The gap between the two gauges is what decides whether three rails will fit. These are the usual pairings, from the scale and gauge figures on Wikipedia’s Rail transport modelling scales:
| Pairing | Standard track | Narrow track | Gap between gauges | Represents |
|---|---|---|---|---|
| HO and HOn3 (1:87) | 16.5 mm | 10.5 mm | 6.0 mm | Standard and 3 ft, as in Colorado |
| HO and HOn30, or OO and OO9 | 16.5 mm | 9 mm | 7.5 mm | Standard and 2 ft to 2 ft 6 in |
| S and Sn3 (1:64) | 22.42 mm | 14.3 mm | 8.1 mm | Standard and 3 ft |
| O and On3 (1:48) | 31.75 mm | 19 mm | 12.75 mm | Standard and 3 ft |
| O and On30 (1:48) | 31.75 mm | 16.5 mm | 15.25 mm | Standard and 2 ft 6 in |
| N and Nn3 (1:160) | 9 mm | 6.5 mm | 2.5 mm | Standard and 3 ft; a very tight fit |
| G (45 mm) and Gn15 | 45 mm | 16.5 mm | 28.5 mm | Metre and 15 in, in large scale |
A quick check that the models are true to scale: in HO, the 6 mm gap between HO and HOn3 track is 6 × 87.1 = 523 mm full size, and the real gap between standard gauge and 3-foot gauge is 1,435 − 914 = 521 mm.
Dual gauge suits small layouts because the most interesting scenes on the real railway, transfer sheds, interchange yards and docks, are compact. Carl Arendt’s Gallery has two pages of plans:
For shunting puzzles to run on a dual gauge yard, see our Inglenook guide; for narrow-gauge micro layouts in general, Carl’s Narrow Gauge Lines and our small layouts guide.
Dual gauge track has three or four rails so that trains of two different gauges can run on it, usually a narrow gauge and standard gauge. Three-rail track shares one common rail; four-rail track keeps both gauges on the same centre line.
When the two gauges are too close together for a third rail to fit, such as metre gauge and 3 ft 6 in, or where both gauges must stay centred, as in tunnels, on bridges and on turntables.
Every place where a rail of one gauge crosses a rail of the other needs its own crossing and flangeway, so a dual gauge turnout has more parts and tighter tolerances than a plain one.
Examples include the Zentralbahn between Lucerne and Horw in Switzerland, the approach to Japan’s Seikan Tunnel, the Baie de Somme line in France and a preserved broad-gauge section at Didcot in England.
The most common pairings are HO with HOn3, OO with OO9, O with On30 or On3, and S with Sn3. In HO the two gauges are 6 mm apart, which scales to the real 521 mm gap between standard and 3-foot gauge.