I make a patch4way_update.patch which allow 2 convoys to enter the 4-way tile only if they do not "conflict" each other.
4way_demo.png
When two convoys are conflict (e.g. N->S and E->W), they cannot enter(reserve) in the same time (see the convoys in the right side of this figure).
4way_test.png
If you add paks, you can reduce the spacing between two digaonal tracks.
4way_demo_with_pak.png
Technically, I add
ribi_t::ribi reserved_dir
convoihandle_t reserved_2
in schiene_t to check the convoys conflicts in 4-way tracks, and update how to resere/unreserve tracks.