Here we go again talking about needing more money to create a 21st century transportation system.

Will it be another endless loop, or will we actually have something to show for it? At least this time the rubber is hitting the road, and coming into focus is how much more money we need to make improvements and how we might pay for them.

The topic du jour: How does a gas tax increase of 15 cents a gallon sound to you?

Not so good to some, and just like that battle lines are being drawn, with reports and polls rolling out fast and furiously. The latest one, out Tuesday, is known as The Transportation Table (T3). The report is from a coalition of 14 groups brought together by the Barr Foundation, which also funded the work.

Their report outlines a policy framework that can be summed up this way: Build a modern rail and bus system that will make people want to get out of their cars. This not only will reduce congestion on the roads, but also benefit the environment. Pay for it, in part, with new tolls and fees that discourage driving and fossil fuel use, and pour that money into transit.

The upshot, said Mary Skelton Roberts, co-director of climate at the Barr Foundation who also leads the foundation’s mobility work, is that “we know what the answers are . . . what we haven’t told people is ‘here is the vision.’ ’’

Sounds reasonable enough . . . if only. While there is growing consensus that more money is needed now and later to achieve transportation nirvana, the real question is whether Beacon Hill has the political will to act. Raising the gas tax is highly unpopular among voters (and there are polls to prove it), and the Legislature has been sitting on a toll expansion study.

There is more agreement across the political spectrum for the so-called Transportation and Climate Initiative fee on fossil fuels that would increase the cost of gas at the pump. Yet it has never been done before and would involve getting other states in the Northeast to levy a similar fee.

Here’s how the various camps are lining up:

In one corner, there’s the $18 billion is enough crowd. That’s the size of a proposed five-year transportation bond bill from Governor Charlie Baker that has the support of some leading business groups such as the Associated Industries of Massachusetts and the Massachusetts Competitive Partnership.

They prefer to borrow their way out of gridlock. A multiyear bond bill has been a staple of transportation funding in the Commonwealth, and this one has some extra goodies such as streamlining the procurement process to speed up repairs. The governor is saying no to a gas tax hike and so are his groupies; instead they are getting behind the climate initiative fee that can raise hundreds of millions of dollars. So what kind of pain would be inflicted at the pump under this scenario? By one state estimate, the average driver could expect to pay any extra $2 to $7 a month.

At the other end of the spectrum is the $50 billion or bust crowd. This is a group that is looking ahead over the next 20 years and supports raising new revenue from a smorgasbord of sources, including the fee on fossil fuels, a hefty increase in the gas tax, and new tolls.

Among those who fall into the “more and more’’ camp are: A Better City, the Metropolitan Area Planning Council, the Kendall Square Association, and Transportation for Massachusetts.

Now if you think $50 billion sounds like a lot of money, think again. If the Commonwealth merely went ahead with its recent vision for a reimagined and electrified commuter rail system, the capital cost of that alone conservatively ranges from $10.6 billion and $14.9 billion.

Meanwhile, peer cities have woken up to the fact that a modern transportation system requires big bucks. Consider that voters in Los Angeles County in 2016 increased the sales tax to raise $120 billion over 40 years for transportation infrastructure. That same year, Seattle area voters increased taxes and fees to help fund a $54 billion transportation package over 25 years.

Here in Massachusetts, messing with the gas tax increase will cause tensions to overflow like a topped off tank —remember, voters rolled back an increase in 2014. The Greater Boston Chamber of Commerce is calling for a 15-cent per gallon increase, while another coalition of business groups, including the Kendall Square Association and the Massachusetts Biotechnology Council, wants at least an 18-cent per gallon increase. Meanwhile, Transportation for Massachusetts, an advocacy group, backs a 25-cent increase.

These groups also back the climate initiative fee on gas, which means consumers could face a double-whammy of hikes at the pump. To avoid that, some are talking about an immediate increase in the gas tax, which then can be replaced by the climate initiative fee when that goes into effect perhaps as early as 2022. It’s something the Worcester Regional Chamber of Commerce backs, as does the Massachusetts Taxpayers Foundation.

“It’s not politically feasible to do both the gas tax and TCI,’’ said foundation president Eileen McAnneny, referring to the Transportation and Climate Initiative fee. “You can have a temporary increase in the gas tax and then TCI.’’

While much of the focus has been on new fees and taxes on gas, a recent analysis by A Better City indicates that an expansion of tolling is where the real money lies.

Consider this: To achieve a goal of $50 billion over the next 20 years, at least half of the money would need to come from new tolls. A Better City, a business-backed transportation group, assumes adding new $2 tolls on Interstate 93 near Boston (both north and south directions), a $1 toll on the interchange of I-93 and I-95, and a $1 toll on highways at state borders (such as I-95 in Rhode Island and New Hampshire).

Currently, drivers pay tolls on the Mass. Pike, the Tobin Bridge, the Sumner/Callahan and Ted Williams tunnels. State and federal laws would need to be changed to add tolls and to redirect that money for transit.

All of this jockeying is taking place as the House prepares to start a serious discussion about transportation revenue. Representative Bill Straus of Mattapoisett and Senator Joseph Boncore of Winthrop, chairs of the Joint Committee on Transportation, agree on this: more money is needed with details to follow.

“I don’t think Baker’s bond bill goes far enough,’’ Boncore told me. Added Straus: “Unabashedly, I say and I believe we do need more revenue.’’

Transportation Secretary Stephanie Pollack says her boss’s $18 billion bond is enough to get the Commonwealth through the next five years. If Beacon Hill wants to think longer term and bigger, Pollack says, there needs to be a discussion on what the additional revenue would pay for.

“If you ask me how much we need, it depends on what we want to do,’’ she told me.

As for the administration’s position on new tolls, Pollack said her department has studied the issue and the report is sitting with the Legislature. “The ball is in their court,’’ she added.

Now some of you might be experiencing Big Dig PTSD, seeing all those dollar signs that begin with the B-word attached to them. But if there’s one lesson we learned from depressing the Central Artery it’s this: go big or go home. Yes, those cost overruns were scary, but in going big, we got to transform the city with the Rose Kennedy Greenway and unlock the real estate value of the Seaport District, one of the hottest markets in the country.

That same opportunity is before Massachusetts again. It’s going to get uncomfortable figuring this out — transformation always is. But if taxpayers are going to pay more, we should know exactly what the money gets us. Map out, for example, the five projects that can get done when you raise my gas tax.

Without that, it’s hard to see how Beacon Hill can get beyond the usual political gridlock.

Shirley Leung is a Globe columnist. She can be reached at shirley.leung@globe.com. Follow her on Twitter @leung.