Congress can always drop the gas tax. That'd help. Bwhahahahahahahahaha...(laughing at my own humor)
It could certainly drop the part of the gas tax that doesn't pay for constructing and maintaining Federal highways.
But, yes, the thought of it doing so is laughable. I mean, what then could it use to blackmail the states into enforcing seatbelt laws, lowering the legal blood alcohol content, etc.?