A REPORT DEVELOPED by the business group A Better City estimates Massachusetts is facing an $8.4 billion shortfall over the next 10 years in bringing state transportation assets into a state of good repair.

The state highway system needs $6.5 billion more than its budgeted revenue over the next 10 years to maintain roads, bridges, and tunnels, according to the report. The MBTA is set for the next five years, but after that it will face a $1.9 billion shortfall, brought on largely by diminishing federal funding and less state borrowing capacity, the report says.

The funding shortfall is just for maintenance of existing infrastructure and doesn’t include money needed to modernize, expand, or decarbonize the state’s transportation infrastructure.  Not included in the funding forecast are proposals to expand the commuter rail system into a subway-like regional rail system, to build South Coast Rail, to connect the Red and Blue Lines, to expand South Station, or to construct the Allston interchange.

The report by A Better City and the UMass Donahue Institute offers a wide variety of options to help close the spending gap. They include raising the gas tax or applying the state sales tax to gasoline purchases; putting a price on the carbon contained in vehicle fuels;  implementing congestion pricing at peak travel periods; adding border or in-state tolls or increasing existing tolls; hiking the fees on ride-hailing apps to match T fares; and launching a vehicle miles traveled fee.

In his first term, Gov. Charlie Baker ruled out major new revenue initiatives to support transportation, but his attitude shifted slightly as he prepared to take office for a second term. He agreed to explore putting a price on the carbon contained in vehicle fuels as part of a multi-state, regional effort and in his budget for the coming fiscal year he proposed an increase in the tax on real estate transfers to support climate change initiatives.

Baker has not raised alarms about a scarcity of transportation funds. He has focused instead on the MBTA’s past inability to spend budgeted capital dollars and his determination to spend $8 billion over the next five years improving the transit system.

A good example of how tight transportation funds are is the $1 billion South Coast Rail project. Baker committed to extending the commuter rail system to New Bedford and Fall River when he ran for office in 2014 and has already committed several hundred million dollars to initial work. But his administration has spent more than seven months trying to figure out how to pay for the rest of the project. Officials say they will come up with the money, but the lengthy deliberations suggest the process hasn’t been easy.