Trains need a certain amount of space or they will crash into each other or into the terrain. They also need to be a certain distance from platforms and won't run to the very end of a track. Clearance doesn't necessarily mean that the node has to be air; this will be explained in the next section.

1. Trains need a 3 metre wide space to travel through. This means the nodes to the left and right of the train need to be clear.
2. Tracks must be at least 1 metre apart, but a recommended distance is at least 2 metres apart.
3. Trains need a 3 metre high space travel through. They cannot fit in any shorter of a space.
4. The height limit is higher on slope nodes, where trains need at least 4 metres of height clearance. To think of it another way, you need the full 3 nodes of clearance as if the train were already at the top of the slope, even when you are at the very bottom.
5. 3 metres of clearance is needed on either side of the slope nodes as well.
6. Where possible, it is preferred that you use 3 metre long slopes instead of the shorter 2 metre slopes.

The diagram below visualises these requirements:

Linetrack boats need 5 metres of horizontal space instead of the usual 3 for trains. The code that handles getting off vehicles is still in need of a bugfix so that the platform is found correctly.

Air always provides clearance. However, which other nodes provide clearance depends on two things:

1. A configuration setting added in 2.4.0, called “Forgiving Collision Mode” (advtrains_forgiving_collision). If that setting is enabled, trains only collide with nodes with “normal” drawtype, which means for instance they won't collide with slabs or leaves.
2. Whether the node is in the group not_blocking_trains. Nodes in this group don't collide at all.
   • Signals, platforms, TCBs, level crossing nodes from advtrains_platform, and platform/line signs from trainblocks/subwayblocks/metrosigns are all marked with this group.
   • LinuxForks' moreblocks fork has gravel slopes that are in this group so that you can lay nice smooth gravel slopes beside your tracks.
   • You can see what is in the group by search group:not_blocking_trains in Unified Inventory (other inventory mods are available).