Top Democrats in the Senate are expected to propose a $250 million investment into a transportation fund as part of their fiscal year 2025 budget that will in turn let the state borrow $1.1 billion over the next five years, a source with knowledge of the plan said.

The overall monetary figure matches what Gov. Maura Healey proposed earlier this year and the House approved in their budget last month. The details of the Senate’s budget emerge as the branch is scheduled to roll out the full spending document later Tuesday.

The increased borrowing ability, state officials have argued this year, will allow the Healey administration to better finance projects at both the Department of Transportation and the MBTA, which is facing a more than $600 million budget gap in fiscal year 2025.

The Senate plans to park $250 million in the Commonwealth Transportation Fund, which primarily collects money from taxes and fees on fuel and motor vehicle sales and transactions at the Registry of Motor Vehicles that is then used to fund projects across Massachusetts.

The investment includes $127 million for the MBTA from a 4% surtax on incomes over $1 million known as the “Fair Share Amendment,” which would double the annual operating transfer to the transit agency, according to the source.

Another $63 million is set aside for debt servicing to leverage increased borrowing capacity. MassDOT is in line to receive $60 million in operating support and $24.5 million is tucked away from commuter rail capital improvements, the source said.

A low-income fare relief program at the MBTA is in line for $23 million of the $250 million investment and water transportation services will receive $7.5 million, according to the source.

Senate budget writers are also including a plan in their fiscal year 2025 budget proposal that Democrats say would allow every Massachusetts resident to attend community college for free.

Lawmakers have been under pressure this fiscal year to rein in spending after months of struggling tax revenues. But the voter-approved surtax on incomes over $1 million has granted Beacon Hill some leeway with proposing new initiatives.

Budget officials also received some welcome news last week, when revenues for April — the largest tax collection month of the year — shot $1 billion above expectations largely due dollars collected under the surtax.