Massachusetts will receive billions of dollars over the next five years as part of a new federal infrastructure package, instilling confidence in Gov. Charlie Baker and one of the U.S. House's top Democrats that the state is poised to make game-changing new investments in how its residents move around the state.

But for transit advocates who spend their days pushing the Baker administration and legislative leaders to focus more closely on improving the MBTA and regional transit authorities, the federal law represents a still-unseized opportunity whose impact will be muted unless Beacon Hill takes a more proactive role.

"Whether or not we use this money in a transformative way is entirely contingent on if the Legislature can get its act together," said Stacy Thompson, executive director of the LivableStreets Alliance.

On paper, the more than $8.6 billion that federal officials expect to flow to the Bay State in formula funds and even more money available in competitive grants represents an enormous opportunity to kickstart momentum on long-discussed projects, such as a passenger train extension into western Massachusetts or a connection between the MBTA's Red and Blue Lines.

Congressman Richard Neal, who chairs the influential U.S. House Ways and Means Committee, is among those who believe the new funding moved the needle on the idea of an East-West Rail link.

Neal, who for years has been a supporter of the proposal, said last week that connecting Boston and western Massachusetts by passenger rail is "one of the most essential infrastructure investments we anticipate making" with the new law in place.

"The money is now available to do that," Neal said during a Greater Boston Chamber of Commerce virtual event. "It's a matter of regional equity, and it could be a game changer for local economies beyond Boston."

Most of the guaranteed dollars headed to the Bay State via the new package, Thompson said, will come as a "reauthorization of the same infrastructure bill that we have had access to since the Reagan administration," albeit at higher funding levels.

Advocates and government officials alike say the difference-maker for many of the most high-profile transportation ideas will be the grant programs. Among the many sources of competitive dollars up for grabs in the new law are $15 billion in Rebuilding American Infrastructure with Sustainability and Equity grants, or RAISE, grants and $23 billion in capital investment grants.

Transit Matters Executive Director Jarred Johnson said Massachusetts will need a more deliberate approach, particularly to move projects from ideas to reality, if its leaders want to capitalize on the available pot of funding.

"The states and regions that are going to benefit from this bill are going to be the LAs, the Utahs, the Seattles -- places that were already doing this stuff and have already shown the political will to have their matching funds in place," Johnson said. "If Mass. wants to make use of this money, they've really got to play catch-up and they've got to have a Legislature and a governor that come together with actual vision for what our transportation system is going to look like."

The T continues to grapple with structural budget shortfalls that have been in place since before the pandemic slashed ridership and fare revenue. Federal emergency aid will close gaps for the next few years, but experts warn the agency could need as much as $1.25 billion in new annual revenue to meet operating and capital needs by the end of the decade.

Massachusetts will receive more than $8.68 billion in formula funding over the next five years as part of the infrastructure law, about $5.3 billion of which would go toward highways and bridges, according to a state-specific breakdown published by the U.S. Department of Transportation.

Another $2.8 billion in formula dollars will go toward public transit improvements in the next five years. USDOT said the first annual installment represents a 40 percent increase over this year's allocation the Bay State received from the 2015 Fixing America's Surface Transportation, or FAST, Act.

Steering money into maintenance alone would go a long way, particularly at the MBTA, where the most recent estimate officials offered in 2019 put a $10.1 billion price tag on replacing all outdated equipment and infrastructure across the system.

"The large message coming for us on this one is that this is a necessary piece of federal legislation," Gov. Charlie Baker said on Nov. 16, one day after Biden signed the law. "States will be able to do a lot of good things with this, many of which are overdue and we expect and anticipate that we'll be able to make some very important and critical infrastructure investment around the Commonwealth over the next five or six years because of it, and we're very excited about it."

At the T, which Baker oversees, the reaction has been a bit less enthusiastic.

MBTA General Manager Steve Poftak said on Nov. 17 that agency officials were still analyzing how much they should expect from the package and what requirements they would face when applying for competitive grants. He threw some cold water on suggestions that the law could prompt a complete transformation of the transit system.

"It is surely going to be additive to our current efforts and we are grateful for the money. I think we're still trying to understand the magnitude of the money we will receive," he said. "I have seen in the popular press lots of thoughtful, creative ideas on how we could spend the money. I do caution that the money may not go that far for some of the aspirational plans that I have seen."

"We have been preparing for this for a long time," Poftak added. "We have a significant shelf full of projects that can be ready to go within the time frame envisioned in this bill. It will not be a challenge for us to come up with necessary, worthy projects. It may be a challenge for us to sequence and prioritize them, but we have been doing a significant amount of preparation for this bill."

The MBTA has been grappling with staffing challenges, too. Poftak said last month that the agency is "struggling to attract the workforce that we wish to have" and that his leadership team was hard at work to accelerate new hires. This week, the T cut bus service, citing a shortage of drivers.

Some advocates worry that a workforce shortage could hamstring the agency's ability to compete for additional federal dollars.

"To get a competitive grant in, it's full-time jobs," Thompson said. "Every single year, the T's operating budget is underfunded, even outside of COVID. So even with this little bump of federal money, we're not set up for success. We're not hiring the human beings that we need to get this done."

Funding questions have long loomed over the East-West Rail connection, which would expand passenger rail beyond its current endpoint in Worcester to provide access to population centers in western Massachusetts.

Before it finalized a study on the topic estimating a total cost between $2.4 billion and $4.6 billion, the Baker administration's transportation department warned that federal funding would be crucial to the future of East-West Rail.

Sen. Eric Lesser, a Longmeadow Democrat who has been one of the most vocal proponents of a western Massachusetts passenger rail extension, said Thursday that he views the infrastructure law's funding for Amtrak and roughly $60 billion in grant funding for intercity rail links as "game-changers."

"For a new project like East-West Rail, it's going to be the competitive grant formula that really makes the difference because the formula funding is likely to go to existing and legacy projects that have maintenance backlogs," he said.

Lesser and other project backers have sparred with the Baker administration in the past, arguing that the Republican and his team have slow-walked work to make the extension a reality and underestimated its impacts.

In October, the Pioneer Valley Planning Council and the Capitol Region Council of Governments published a report estimating that the Baker administration's methodology omitted demand for the rail line from Hartford, Connecticut. Adding those prospective commuters, the groups said, would boost projected ridership by 54 percent.

Asked if he agreed with Johnson and Thompson that the Legislature should take a more proactive role to maximize the infrastructure law's impact, Lesser shifted some of the onus to the administration.

"In theory, we could continue to ratchet up (pressure) legislatively, but make no mistake: at the end of the day, the application is filed by the executive branch, it's not filed by the legislative branch," he said. "We do have a lot of tools in the Legislature at our disposal to push the point and not take no for an answer, but at the end of the day, we do need them putting the best application forward possible."

Baker and Lt. Gov. Karyn Polito announced last week that they will not seek a third term in office, creating a wide-open race for the corner office in 2022 that could reshape the administration's approach to public transit funding.

Although Biden signed the new infrastructure law, the funding will not begin to flow until Congress enacts an appropriations bill, MassDOT Director of Capital Planning Michelle Ho said on Wednesday. She added that it could be "challenging" for the Bay State to program all of the new transportation dollars in the federal fiscal year that ends Sept. 30, 2022, which could push additional key decisions onto the next occupant of the corner office.

In Thompson's view, Massachusetts does not have the flexibility to wait for a changing of the guard.

"If we are waiting until January of 2023 to start having this conversation, we've already missed the boat and forty-nine other states have already sucked up billions of dollars that could have been ours," she said.