freebeer
So maybe there would be a weight limit posted, or a height limit somewhere?
Generally a router engine would need to be fed with such specific information, rather than a generic idea of, oh use that route instead, it's better, without specific grounds.
Here the only visible difference I see is the displayed width of this road being smaller than the two nearby county roads, which could have some influence, but clearly not enough.
I presume it is also not a private road with restricted access.
I am neither a road, nor a routing expert, so perhaps someone else can suggest other improvements.