But some skeptics said they’re wary of carving gaps into environmental guardrails, even in the name of greener transportation. They question whether environmental regulations are such a substantial hindrance to getting projects over the finish line.

“There are a lot of agencies who simply don’t want to do things, don’t want to spend money, don’t want to make major investments, and they use the environmental process as an excuse for not making them,” said Fred Salvucci, the Massachusetts secretary of transportation under former Governor Michael Dukakis.

Public environmental reviews, codified by the Massachusetts Environmental Policy Act (MEPA) and related regulations, are triggered when projects meet specific thresholds,such as if they alter a certain amount of land, generate a certain volume of pollutants, add a certain length of road, and so on.

Projects with a bigger expected environmental footprint can require more thorough environmental impact reports that flesh out in detail what a project might do to the environment and what would be done to mitigate those effects.

State law also mandates impact reports for any potentially damaging project within a mile of an environmental justice population, historically overlooked areas with large concentrations of low-income households, non-English speakers, or minority communities.

The impact reports can be exhaustive,demandingportraits of a work site’s topography, habitats, and soil, among other minute details. The draft environmental impact report for the Allston Multimodal Transportation Project, a behemoth effort to reorient part of the Massachusetts Turnpike, spanned more than 600 pages (without appendices).

This process can hamper projects that could greatly benefit the environment, said Crighton, who last year put forward a bill that aims to exempt zero or low-emission rail projects from the need to “produce environmental impact reports.”

“When you look at these diesel commuter rail train locomotives that are spewing out diesel fumes and particulate matter into environmentally sensitive areas, into our backyards, I think most folks would recognize that there is a benefit there, and one that’s worth expediting the process for,” Crighton said.

The T is in the early stages of electrifying its commuter rail service in the hopes of slashing emissions and improving service. It plans to deploy battery-electric locomotives along the Fairmount Line in 2028.

In recent years, the T has undergone MEPA reviews for track improvements in Billerica and a commuter rail maintenance facility in Hyde Park, according to the state’s MEPA database. MEPA analysts have also scrutinized a pedestrian and bike path in Williamstown pitched by MassDOT.

A related bill, presented by state Senator Cynthia Stone Creem, seeks to exempt other types of transit projects from MEPA review, including new bike facilities and light rail and transit lanes within existing rights of way.

These types of projects “are all things that we should be able to help and move along,” said Creem. “Having a better and cleaner transportation option allows us to reduce vehicle emissions that pollute our waterways and harm natural habitats.”

Costs and timelines of the review process can vary, experts said.

“Each project is so context specific,” said Seth Gadbois, a clean transportation staff attorney at Conservation Law Foundation, a Boston-based environmental advocacy group.

According to state rules, the public has 30 days to review the first round of environmental assessments. Environmental impact reports, the next, more intensive review stage, are subject to a 37-day public review period.

The process can get prolonged by the state if it’s dissatisfied with the reviews, or by legal challenges filed by those displeased with a report’s approval.

Working through impact reports can take a minimum of nine to 12 months, and cost $350,000 to $1 million,housing developers and development experts told a state housing commission, according to a February 2025 government report.

The state enacted MEPA in the 1970s. Bearing a nearly identical name to its federal cousin, the measure was born amid a burgeoning public consciousness about the well-being of the environment, and the government’s role in protecting it from the most destructive byproducts of human industry.

“MEPA exists to make sure that decision makers, communities and the proponents of any given project are aware of all the potential consequences, positive or negative, and that we have that view so that we can address negative consequences accordingly,” Gadbois said.

That information, some advocates said, is vital.

“The neighborhood that you live in should have information[about] how different developments impact their public health. That’s something that we advocated and fought for, for a very long time,”said Dwaign Tyndal, executive director of Alternatives for Community and Environment, an environmental justice advocacy group based in Roxbury.

Massachusetts is confronting the potentially cataclysmic consequences of a warming climate.Thestate government in 2021 pledged to achieve net-zero greenhouse gas emissions by 2050.

Achieving that goal, experts and advocates said, hinges on changing the way Massachusetts moves. The transportation sector is responsible for 37 percent — the largest share — of the Bay State’s emissions, according to government assessments. Light duty passengers vehicles — cars, SUVs, and other four-wheel vehicles below a certain weight threshold — generate the greatest portion of those emissions.

State political leaders have sought to slacken MEPA’s rigor before. This past fall, the Healey administration announced tweaks to the MEPA process designedto speed up housing construction. The amendments allowed some types of housing projects to forego the more strenuous stages of MEPA review.

Some doubt doing away with MEPA assessments for some transportation projects would speed up much at all.Pete Wilson, senior policy director of Transportation for Massachusetts, suspects the time savings from a MEPA exemption would be relatively meagre, not nearly enough to justify foregoing valuable public discussions.

“Removing the MEPA requirement,” Wilson wrote in an October letter to the legislature, “would have minimal impact on streamlining the permitting process,” given all the other state and federal regulations projects must clear to move forward — the National Environmental Policy Act, the Clean Water Act, Massachusetts Historic Commission rules, among others.

“Time is money,” Wilson acknowledged. But, he added, “faster doesn’t always mean they’re better.”

Crightonsaid he’s speaking with advocates to adjust the bill’s language.He said he knows his bill isn’t a “silver bullet.”

But,Crighton said,“you have to chip away” at reform.

Jaime Moore-Carrillo can be reached at jaime.moore-carrillo@globe.com.