Some additional context by you to accompany this question may help narrow down the subject and lead to better ideas.
Your paper may start with a good purpose or declaration of what you will cover (or not discuss).
For instance, you might identify the federal/state/local laws covering highway maintenance, as a way to show who must spend money. Example - WA state law says for towns above 10,000 population are required to maintain state roads within their city limits. So Seattle is somewhat on the hook to maintain the Viaduct.
Another example - who owns the right of way may have to maintain it. When a city incorporates a portion of county land, by operation of law the right of way automatically transfers to the city and thus some maintenance responsibility accrues.
Maintenance may imply treatment - for example, stormwater runoff from federal highways may have to meet state or local water quality & quantity treatment standards. This accounts for payment by the federal & state government to local cities such as Bellevue, based on the area of impervious surface.
Take a look at the federal highway administration website for good ideas.