Fuel excises do not get allocated directly to some kind of "road budget", they go into general revene. Almost all of it can be accounted for in corresponding fuel tax credits, three quarters of which go to mining companies. From memory the difference in 2019 census was like 100mil, so 7.8billion came in from fuel excise, 7.7billion went back out in fuel tax credits.

In essence, everyone pays for federal roads, road user or not, and municipalities pay for local roads. Except for larger state funded projects, which often receive federal assistance. Fuel taxes are a trivial component to infrastructure upkeep, is my understanding.

Another myth is that vehicle registration pays for roads, vehicle registration goes entirely to running the vehicle registration apparatus, that's all.