Is there a recommended road width, e.g. 2 or 4? Does the width of the road have any impact on path finding performance, or congestion?

Drones will try to do a low resolution pathfind (on 2x2 tiles),
If that fails they will try again with 1x1 resolution.

So 2 wide roads should help the pathfinder

Also they kinda skid/drift around corners, so a wider road gives them more space to drift around

are these 2x2 tiles identical with the grid for rails, or can they be at any even or odd coordinates to have beneficial effects?

i also found that it helps them hitting the loading and unloading tiles when there are road tiles on at least 2 or better yet on all 3 sides of those load/unload tiles.

concerning congestion: since they all pass through each other and also don't hit the player (and yet i always sidestep when they come towards me, LOL), i see no reason to build wider roads only because of heavy traffic.

Ok just to make sure I understand correctly width 2 better than 1 and 2 better than 4 or larger.
And I guess depots should be build directly on the road instead of 1-2 tiles offset.

It can be any 2x2, it ensures there is a path on the 2x2 resolution.