Hi BiffBish,
I'm sorry for not beeing able to reply earlier. The bug you mention is something i cannot do much against, as the "gap" is caused by the way Factorio draws tiles.
For straight diagonal lines i use the "inner-corner" drawing tiles that are placed in a way to create the illusion of an continuous line. This only works because the tiles with diagonal lines have a higher "tile layer index" and are drawn above the normal asphalt tiles. The tiles with corners don't connect to this tiles and are drawn separately - thus creating a visible gap. The double line tiles are very wide, which makes this gap clearly visible.
I'm sorry, currently i cannot do anything against this issue.
