Double oval: two trains at once

Benjamin | TrackDrawer.com · published 2 November 2026

A double oval is an oval with a second oval inside it, on a radius that is smaller by exactly the track spacing of your system. Each loop carries its own train, and a crossover lets a train move from one loop to the other. The outer loop sets the size of your baseboard: with Märklin C track R2/R1 you need at least 101.5 cm of depth, with R3/R2 117 cm.

Two loops at one spacing

With most sectional track, each radius lies exactly one track spacing outside the next. On C track, R1 is 360 mm, R2 437.5 mm and R3 515 mm: 77.5 mm further out each time, the same offset the C track turnout gives with its matching curve. Where that figure comes from is explained in track spacing.

Give both loops the same straights and they stay the same distance apart all the way round, on the straights and in the curves. That is how the Auto-designer lays double track as well: the inner loop on the next smaller radius whose step equals a track spacing of the system, with the same straights as the outer loop. An example from a run on 240 x 120 cm with C track: "Double track R3/R2", 60 pieces and 10.83 m of track. Each loop has twelve curves, and each straight side is 1211.7 mm long.

How deep does your baseboard need to be?

The inner loop is never the problem; the outer one is. Its depth is twice its radius plus the track bed width, and then the margin comes on top. The table gives the smallest pair per system whose radius step equals the track spacing.

In H0, then, a double oval is never much less than a metre deep. It does not fit on the popular 180 x 90 cm; what does fit there is covered in an H0 layout on 180 x 90 cm. On Märklin Z, R1 (145 mm) lies 50 mm inside R2, twice the track spacing, so a double oval at the standard spacing starts at R3/R2.

What the Auto-designer fits on 240 x 120 cm

TrackDrawer had the Auto-designer plan for each H0 system on 240 x 120 cm with a 50 mm margin, from a typical drawer of track (per radius a full circle plus four curves, eight each of six straight lengths, three left and three right turnouts, four matching curves, four compensation pieces, one crossing and three buffer stops where the system has them).

Two systems are missing. On Kato Unitrack H0 the radii are 60 mm apart, while the track spacing is 74.6 mm. On Hornby the step between R1, R2 and R3 is 67 mm each time, just off the track spacing of 66.68 mm; the R4/R3 pair does match, but at 127.2 cm it is too deep for this baseboard. The Auto-designer only lays a double oval where both loops sit exactly at the track spacing, so it found none there.

The crossover

A crossover is a pair of turnouts, one in each loop, whose diverging routes join each other directly. On C track, two 24.3° turnouts on R437.5 together shift the track sideways by exactly 77.5 mm over a length of 360 mm. On each track the crossover therefore takes up 360 mm: the 188.3 mm turnout plus a 171.7 mm compensation piece.

Watch the direction of travel. If both trains run round in the same direction, one crossover only takes a train from one track to the other. For the way back you lay a second crossover, mirrored. The Auto-designer adds a crossover when the turnouts in your stock bridge exactly the gap between the loops with their diverging route and the straight is long enough.

Electrically: two circuits

On analogue control you want a controller for each loop. The two loops then have to stay electrically separate, including at the crossover. On two-rail you gap both rails between the two turnouts; on Märklin three-rail you gap the centre conductor. With digital control one command station feeds both loops and you drive each train by its own address, so no separation is needed just to run.

A crossover between two loops running in the same sense is not a reversing connection: the left rail stays on the left. Only when you join the outer loop to the inner one in a way that brings the train back the other way round do you get the problem of the reversing loop. The TrackDrawer check flags that on two-rail systems.

Running two trains

• Left or right. On a real double-track line, trains in the Netherlands and Germany normally run on the right, in Belgium, France and Britain on the left. If you run the two trains in opposite directions, they pass each other twice per lap.
• Long coaches in the curve. On the inner loop the ends of a long coach swing outwards; on the outer loop its middle swings inwards. At the standard spacing of sectional track that usually clears, but laying flexible track closer together is risky.
• Adding a station. On a straight side you can hang a passing loop or a siding on the outside, as the variants above show.

Frequently asked questions

Isn't a passing loop enough for two trains?

For two trains that take turns, yes. With a double oval both can keep running at the same time, without one waiting for the other.

Can I turn an existing oval into a double oval later?

Yes, if your baseboard is deep enough for the outer loop. Keep your current loop as the inner one and lay a loop outside it on the next radius, with the same straights. How to extend a single oval step by step is covered in the oval.

Try it yourself

Enter your curves in two radii and let the Auto-designer lay out a double oval, with or without a crossover.