I don't think changing the federal part of the gas tax is going to change much:

FHWA coughs up 80% of the cost of highway construction projects, the states need to pony up the matching 20%. At the start of the fiscal year, the 20% is in the transportation budget. Later on, that pot proves too tempting and the money is used to plug hole in the general fund budgets. The Feds then rescind their 80% and the roads deteriorate further.

Boosting the fed contribution to 100% will most likely set up "leakage" that will make Medicare fraud look like pocket change because there will no longer be any local incentive that the project is done right.