iStock photo

The pact being developed by Massachusetts and other East Coast states to cap carbon emissions from vehicles could add up to 17 cents to the price of a gallon of gas, according to the newest estimates, but could also generate more than $500 million in revenue for state government in Massachusetts.

Leaders from a coalition of eastern states, including Massachusetts, have been working for over a year to develop a regional “cap-and-invest” program to reduce carbon pollution from cars and trucks and generate the resources needed to expand clean transit options and improve public health.

The effort, known as the Transportation Climate Initiative, has also become a central part of Gov. Charlie Baker’s transportation and climate agenda, with the administration proposing to earmark half of all proceeds generated toward improving public transit.

But the coalition already began to splinter Tuesday in light of the newly forecast economic impacts, with New Hampshire Gov. Chris Sununu announcing that his state would not participate.

“We are already taking substantial steps to curb our carbon emissions, & this initiative, if enacted, would institute a new gas tax by up to 17 cents per gallon while only achieving minimal results. This program is a financial boondoggle and the people of NH will never support it,” Sununu wrote on Twitter.

The coalition, chaired by Massachusetts Energy and Environmental Affairs Secretary Kathleen Theoharides, released a draft memorandum of understanding on Tuesday that states would be asked to sign onto next spring once it is finalized.

The officials involved in the effort are eyeing a reduction in emissions of up to 25 percent by 2032, but it will come at a cost.

States in the coalition are exploring three scenarios for capping emissions from motor gasoline and on-road diesel, with a final cap proposed after a public comment period ends on Feb. 28.

The plan to reduce carbon emissions from vehicles by 25 percent would add an estimated 17 cents to the price of a gallon of gas at the pump starting in 2022. If states elected for a smaller reduction goal of 22 percent, the cost per gallon, based on the group’s modeling, would drop to 9 cents.

The third option presented is for a 20 percent emission reduction by 2032 at a cost to drivers of 5 cents per gallon.

Theoharides said TCI represents a “chance to really make a global impact on emission reductions.

“The thing that is important is that while the reference case does show 19 percent due to clean vehicle standards and the adoption of electric vehicles, those reductions are not guaranteed and they could be as low as 6 percent. What this policy does is lock in those reductions,” Theoharides said.

The new economic forecasts also figure to play heavily into the upcoming debate that House Speaker Robert DeLeo has planned for January to generate new revenue for transportation.

Several of his top deputies have suggested a gas tax hike would be high on the list of options.

The concept, however, has been coming under increasing fire from a small group of Republican legislators and small business groups.

Rep. Timothy Whelan, a Brewster Republican, and Rep. Marc Lombardo, a Billerica Republican, both submitted public comments to the coalition arguing that the Legislature should get to vote before Massachusetts joins any partnership.

Sen. Marc Pacheco and the Baker administration have said the Legislature would not need to vote on participation because the legislators authorized the administration to pursue regional market-based approaches to fight climate change in the 2008 Global Warming Solutions Act.

A MassINC poll released Wednesday found that a majority of registered voters in Massachusetts, Connecticut, Maryland, New York, New Jersey, Pennsylvania and Virginia — the largest states in the coalition – strongly or somewhat support their home state’s participation in the Transportation and Climate Initiative.

In Massachusetts, 68 percent of the 629 respondents said they support the program, compared to 21 percent who oppose it and 11 percent who are unsure, according to the poll, which was sponsored by the Barr Foundation and conducted before the latest estimated impacts on gas prices were known.