How to plan a LEGO DUPLO train track from the pieces in the box
DUPLO train track is a small system with very regular geometry, which is why a box of it is so satisfying to plan. Every curve turns 30 degrees, so twelve make a circle, and every curve advances the line by exactly the length of one straight, 128 mm. That one fact is why almost every DUPLO layout you can draw closes exactly, with no fudging at the joints.
The pieces and their measurements
- Straight: 128 mm from joint to joint, 8 studs.
- Curve: 30 degrees on a 256 mm centreline radius. A circle of twelve is about 58 cm across on the outside.
- Points: a wye. Both arms are routes, and the lever picks one. There is no left-hand or right-hand version.
- Level crossing: a straight with a road across it, the same 128 mm.
- Buffer stop: caps the end of a siding. A set of points without one leaves an open joint, and a train will run off the end.
- Bridge (10872): two ramps and two half arches, 1024 mm in all, exactly eight straights, with room for a line to run beneath the middle.
What comes in each set
| Set | Track |
|---|---|
| 10425 Train Tunnel and Tracks | 1 straights, 10 curves, 1 points, 1 buffer stops, 1 hill ramps |
| 10426 Train Bridge and Tracks | 9 straights, 1 bridge |
| 10427 Interactive Adventure Train | 2 straights, 12 curves |
| 10428 Big Interactive Community Train | 4 straights, 15 curves, 1 points, 1 hill ramps |
| 45025 Coding Express | 12 straights, 14 curves, 2 points, 4 buffer stops, 1 level crossing |
| 10872 Train Bridge and Tracks | 8 straights, 1 bridge |
| 10874 Steam Train | 4 straights, 12 curves |
| 10875 Cargo Train | 3 straights, 14 curves, 2 points, 2 buffer stops, 1 level crossing, 2 hill ramps |
| 10882 Train Tracks | 1 straights, 10 curves, 2 points, 2 buffer stops, 1 level crossing |
The 2025 sets use the same rails as the 2018 ones. Their straights with plates on the side are ordinary 128 mm straights that an action brick sits on, and the new bridge in 10426 runs the same 1024 mm as the old one. Track from before 2018, dark grey rather than light grey, is a different story: the curves do not close cleanly, and the planner marks those sets as old track.
Start with the oval
The 10874 Steam Train box makes one thing: an oval of twelve curves with two straights a side. It is the layout on the box, and it is where every bigger layout starts, because a second set adds sidings, a second loop or a bridge to it.
Add points, and a stop for every siding
Adding 10882 Train Tracks gives you two sets of points, two buffer stops and a level crossing. The picture on the back of that box puts a siding off each side of the oval. The rule to remember is that every spare arm of a set of points needs to lead somewhere: either back into the track, or to a buffer stop. The planner will not offer a layout with an arm left hanging.
A second loop, and a figure of eight
Two loops joined through the points need twenty-four curves the ordinary way, which is two 10874 boxes plus the points from a 10882. With only twenty-two curves, 10874 and 10882 together, the trick is to let each set of points stand in for a curve of its loop, so the loops join along the tangent at the toes. The planner knows both arrangements. A figure of eight needs the bridge from 10872 so the two lobes can cross.