Chapter 90 is a state law that defines how state highway funds are distributed to local MA communities. It isn't MassDOT or federal highway funds.

Each year the state legislature appropriates (passes a budget with) a certain amount of money for MassDOT and for chapter 90.

MassDOT and sometimes individual communities can (and do) also apply for federal highway funding for projects. It is sometimes a bit more complicated - big projects are usually a mix of state and federal funds (plus sometimes local funds), and MassDOT also plans for a certain amount of federal highway funds each year (much like towns plan for a certain amount of chapter 90 funds). But we sunk many years of what would be MA's federal highway allotment to pay off the big dig, which probably put us way behind on federal highway funds available for the rest of the state.

As the top comment says, US numbered highways are not maintained by the federal government. US route 5 is just a federal designation for maps to help people get around, not any federal claim of ownership or responsibility for repairs.

US 5 might be locally owned or state owned - or even a mix; even if the towns own the "road", often the state owns/maintains the bigger bridges. Who owns it pretty much defines who is responsible for maintaining it. If the state, then MassHighway (for example, they definitely own I91). If the local town owns it, then it is the local town that needs to fix it, either through chapter 90 funds, local tax funds, or they can apply for a federal grant (often hard to get, you are competing with everyone else in the US).

But in the end - your local planning office, highway department, or state rep might be the best people to ask about who is responsible for fixing US5, and to ask why it isn't being fixed.

Hope that helps a little.