The dogbone: a long run on a narrow baseboard

Benjamin | TrackDrawer.com · published 30 October 2026

A dogbone is a continuous run with a turning curve at each end and two parallel tracks in between: seen from above it looks like a chew bone. It gives you a long continuous run on a long, narrow baseboard or along a wall, and the two middle tracks look like a double-track main line. At the ends the baseboard has to be as wide as the turning curve: twice the radius plus the width of the track bed, plus a little margin.

What a dogbone is

Start with an oval and squeeze it in the middle. The two straight sides come close together, while the curves at the ends keep their full radius. What is left is a bone: two round ends and a narrow waist. Electrically and in operation it is still an ordinary closed loop. The train always circulates in the same sense and passes the same point in the same direction after every lap.

That is where a dogbone differs from a reversing loop. In a reversing loop the train comes back onto the same track facing the other way, and on two-rail DC that causes a short circuit. A dogbone does not have that problem, as long as you do not join the two middle tracks with a crossover. If you do, each end becomes a reversing loop and you have to isolate it.

Oval, dogbone and folded figure eight

• Oval: two half circles of 180 degrees with two straights in between. The straights are exactly twice the radius apart. The space inside is often empty or calls for a station.
• Dogbone: the ends turn through more than 180 degrees, so the straights move towards each other. The middle becomes narrow, the ends stay wide. The train keeps the same turning direction all the time.
• Folded figure eight: similar to a dogbone, but one end is mirrored. The tracks then cross in the waist, on a flat crossing or over a bridge, and the train changes its turning direction every half lap. That adds variety, but needs a crossing or a change in level.

On a rectangular baseboard an oval and a dogbone are equally wide: both need a curve of twice the radius at the ends. The difference is what you do with the middle. A dogbone frees the waist for a narrow strip along a wall, and the two tracks running side by side give the look of a real main line, with trains passing each other. In an L-shaped or long, narrow room, such as a shelf layout along the wall with a wider end at each side, a dogbone is often the only way to get a continuous run.

Why the turning curve is wider than the two tracks

In the waist the two tracks lie close together, at the track spacing or a little more. On Märklin C track that spacing is 77.5 mm, so with a 40 mm track bed the waist is barely 12 cm wide. A curve that turns the train round, however, needs a diameter of twice the radius: 875 mm on C track R2. Those two sizes do not match.

The answer lies in the end. One track runs straight into the curve. The other first swings outwards with a short reverse curve and runs off at an angle until it is far enough from the first track to close the big curve. The curve at the end therefore turns through more than 180 degrees: 180 degrees plus the angle of that reverse curve. TrackDrawer's Auto-designer builds its basic shape exactly like this, with an end of 180 degrees plus one curved piece and a reverse curve of one curved piece.

That swing costs length, and it is the key lesson of the dogbone. We worked it out for C track R2 with a waist of 77.5 mm:

• with a reverse curve of 30 degrees (one curved piece) one end is about 2.05 m long, measured from the outside of the curve to where both tracks are parallel again;
• with a reverse curve of 60 degrees (two curved pieces) it is about 1.40 m.

A true dogbone with a narrow waist on R2 therefore soon needs 3 to 4 m of length. On a shorter baseboard the middle tracks move further apart: if you stay within 2 m of length, a 30-degree reverse curve leaves roughly 70 cm between the two tracks. That is still a usable plan, it is just more of an oval with bulging ends than a slim bone.

How wide does your baseboard need to be?

The width of the baseboard at the ends is the outside size of the turning curve: twice the radius plus the track bed width. Add a few centimetres of margin at each edge so nothing hangs over. The table gives those sizes for some systems and radii in our catalogue.

For a dogbone, pick a larger radius than the minimum if you can: at the end the train runs through a long curve of more than a half circle and then through a reverse curve, and long coaches run more smoothly there on R2 than on R1.

What the Auto-designer lays on 200 x 120 cm

With the typical box of Märklin C track (a full circle plus four curves per radius, eight of each of the first six straights, three left and three right turnouts, four matching curves) and a 5 cm margin all round, the Auto-designer finds, among others, on a 200 x 120 cm baseboard:

• "Dogbone on R2, plus siding and yard": 37 pieces, 6.31 m of track;
• "Double track R3/R2, plus siding and yard": 56 pieces, 10.76 m of track;
• "Station with two platforms on R2": 36 pieces.

The dogbone fits because the turning curve on R2 is 101.5 cm wide including margin, and 120 cm is enough. For comparison: on 180 x 90 cm a plain "Oval R1" comes to 22 pieces and 4.11 m of track. The dogbone on the larger baseboard gives one and a half times the running length of that oval, with a siding and a yard on top. If you want more track, the designer goes for double track, but that also takes many more pieces.

Tips for your own dogbone

• Put a station or a few passing loops in the waist: the tracks already run side by side there and look like a through main line.
• Hide one end behind a backscene or in a tunnel, so the line seems to lead off into other country.
• An end below the baseboard, as a fiddle yard with storage sidings, turns the dogbone into a run with a beginning and an end.
• Keep to your system's track spacing in the waist, so long coaches do not touch.

Enter your own track and baseboard size, and let the Auto-designer work out whether a dogbone fits and how much track it gives you.