That didn’t answer the question
> whether they're completely treating federal roads separately or using it for the total, etc
The tax does not distinguish types of road, much like a gas tax does not.
The context we were in is Utah gas taxes and how much it affects road funding that Utah does. Were you referring to something different? I would assume that Utah gas taxes, if they are intended to fund road work, would go towards state roads in Utah (but that's just an assumption, which is why I was interested in the source).