By David Abel 

The Boston Globe

Massachusetts and 11 other Northeastern and mid-Atlantic states released a framework agreement on Tuesday for a “cap-and-invest” system to curb transportation emissions, the nation’s largest source of greenhouse gases.

The plan, which includes Washington D.C., seeks to cap vehicle emissions from Maine to Virginia and would require hundreds of fuel distributors in participating states to buy pollution permits for the carbon dioxide they produce. That cap would decline over time, mirroring a similar compact that has reduced power plant emissions in the Northeast.

The current proposal does not include key details, such as how much pollution would be allowed and how quickly the caps would decline. That information is slated to be released later this year.

But state officials hailed the agreement as a milestone that would curb emissions of more than 45 million registered vehicles and said they hoped many of the states would sign a more detailed agreement next spring. Transportation emissions make up 28 percent of US greenhouse gas emissions and 40 percent of the region’s emissions.

“This entire project aims to reduce emissions, improve public transportation, equity, mobility, and engagement,” said Kathleen Theoharides, secretary of the Massachusetts Executive Office of Energy and Environmental Affairs, who has chaired the effort known as the Transportation Climate Initiative.

One of her priorities has been to ensure the agreement serves the interests of lower-income populations as well as rural communities, where there are fewer transportation options, she said.

“The communities most impacted by climate change are often the least able to respond,” she said.

If approved, the pact would be modeled after the Regional Greenhouse Gas Initiative, a nine-state regional cap-and-invest system for power plant emissions. Widely seen as a national model, the mandatory market-based program has helped reduce power plant emissions from Maryland to Maine by about 40 percent below 2005 levels without raising average electricity prices.

In a cap-and-invest program, companies would be required to pay for the pollution they emit. The price would likely rise as the amount that each company is allowed to produce would decline over time. Groups that represent fossil fuel interests have expressed skepticism about the plan, concerned it will increase transportation costs.

Theoharides said the states are still negotiating over whether to place requirements on how the proceeds from the pollution permits, also known as allowances, could be used. The goal is to invest the money in a range of transportation-related projects, such as public transit, carpooling, and subsidies to accelerate the adoption of electric vehicles, she said.

Massachusetts has already pledged to devote half of the proceeds to the Commonwealth Transportation Fund, where it would be used to reduce emissions and shore up the state’s transportation system against rising sea levels and other consequences of climate change, she said.

In addition to Massachusetts, Maine, New Hampshire, Rhode Island, Vermont, Connecticut, New York, New Jersey, Pennsylvania, Delaware, Maryland, and Virginia are participating in discussions. North Carolina is also considering joining.

If all the states were to join, the coalition would constitute more than one-fifth of the nation’s population and a quarter of the country’s economic output. If the states formed a single country, they would rival Japan as the world’s third largest economy.

One group that has long called for a regional agreement on transportation emissions estimated it could raise more than $5.5 billion over a decade and generate more than 50,000 jobs in Massachusetts.

“The framework agreement is a major achievement for this bipartisan group of states,” said Jordan Stutt, carbon programs director for the Acadia Center, an environmental advocacy group in Boston.

But Stutt and others said its effectiveness will depend on the details.

“The TCI program will be a success if this framework is paired with an emissions cap that reflects the urgency of the climate crisis,” he said. “We’ve run out of time for anything less than that.”

Chris Dempsey, director of Transportation for Massachusetts, urged the states to take action soon.

“Massachusetts residents deserve a robust and equitable regional agreement that will clean up our air and enable new investments in our transportation system statewide,” he said.