====== Space Requirements ======

===== Clearance for Trains =====
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.

  - 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.
  - Tracks must be at least 1 metre apart, but a recommended distance is at least 2 metres apart.
  - Trains need a 3 metre high space travel through. They cannot fit in any shorter of a space.
  - 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.
  - 3 metres of clearance is needed on either side of the slope nodes as well.
  - 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:

{{:usage:spacerequirementsforadvtrains.png?400|}}

{{:usage:spacerequirements2.png?400|}}

===== Clearance for boats =====
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.

===== Conditions for clearance =====

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

  - 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.
  - 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' [[https://git.bananach.space/moreblocks.git|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).