Vertical clearance
Work in progress: This section is still a work in progress — content is being added and revised continuously.
What is checked? Where one track crosses another in height (overpass, tunnel under the second level), the plan check verifies that enough room remains between the lower railhead and the underside of the upper roadbed for your vehicles. It checks the turns of a helix against each other in the same way, even with turnouts in the helix, a branch that leaves under the turn above, and a track that crosses over itself (figure eight with an overpass).
Why does it matter? The required clearance height is chronically underestimated: vehicle height per NEM plus roadbed board plus ballast — and considerably more with catenary. An underpass that is too low is barely correctable after the build (half the layout sits on top of it).
How to fix it: Increase the height difference of the crossing tracks (lengthen the ramps — or split the difference across both tracks), use a thinner roadbed at the crossing, and tick the “Catenary” option only if wire actually hangs (it applies to the whole plan).
Numbers & defaults: vehicle height per NEM 102 (H0: 45 mm, with catenary 59 mm, editable) + roadbed thickness 12 mm.