Maryland Gov. Larry Hogan’s administration says a project adding toll lanes to Washington-area highways would reduce air pollution, along with congestion. But a researcher whose study was used to support that conclusion said it’s not that simple.

Hogan is pushing an $11 billion expansion of the Capital Beltway and Interstate 270, adding toll lanes that a private company would build and manage for the state. He says it’s needed to reduce “soul-crushing” traffic.

In documents outlining the project and its benefits, state transportation officials suggested it would help Montgomery and Prince George’s counties reduce an excess of ozone pollution and other toxins. They cited a 2011 study in the academic journal Atmospheric Environment as proof.

Stuart Batterman, second author on the study, said it’s true that reducing congestion and limiting vehicle idling can sometimes cut pollution. But that doesn’t mean adding the highway lanes will clean the air, the University of Michigan professor of environmental health said.

The research paper “should not be used to suggest environmental benefits” from the project, Batterman wrote in an email to state officials Monday. He repeated his assessment in an interview with The Baltimore Sun.

The Board of Public Works is set to vote on the highway public-private partnership Wednesday.

In a statement, Maryland Department of Transportation spokeswoman Erin Henson said the administration’s assessment of the highway project’s impact on greenhouse gas emissions is based on the same model that Batterman recommended the state use, and that it shows a 28 percent decrease in emissions if vehicles increase their speeds from 20 mph to 50 mph.

The model shows that “greenhouse gas emissions decline as speeds increase,” she said. “Managed lanes allow more free-flowing travel.”

But Batterman said a more thorough analysis is needed to determine the project’s environmental impact.

“It’s complex,” he said. “What was done was to really oversimplify.”

Batterman spoke up at the insistence of Josh Tulkin, executive director of Sierra Club Maryland, who contacted the professor after seeing the study cited in the report and reading the research. When Batterman explained that the study was being improperly cited, Tulkin asked him to put it in writing, both men said.

Tulkin said he thought the Hogan administration needed to be held accountable for its statements.

“They’re claiming environmental benefits, and they have no data,” he said.

In the report, state transportation officials estimate that delays on the two highways already multiply travel times three or four times compared with travel times when there isn’t traffic. And they project those travel times to grow 25% longer by 2040 without more lanes being added.

By reducing congestion, the new toll lanes would cut vehicle emissions, officials said. Those emissions drive smog-inducing ozone pollution.

“Studies have shown that roadway congestion, characterized by slower speeds and increased acceleration/deceleration leads to higher concentrations of other harmful air pollutants such as carbon monoxide, nitrogen oxides and volatile organic compounds especially near the roadway,” the officials wrote.

Batterman said it can sometimes be true that idling of vehicles in stop-and-go traffic can contribute to higher emissions, especially during winter, when temperatures can get too cold for emissions control technology to work effectively.

On the other hand, he said, vehicles tend to generate more pollution per mile when moving at faster speeds, because that requires more power.

The state’s analysis, he said, doesn’t account for a likely increase in the number of vehicles traveling on the widened highways because of induced demand, which could offset reductions in congestion-related emissions. Opponents of highway expansion argue that people will be more likely to choose travel by car or truck over transit, biking or some other alternative if they perceive less of a headache from traffic.

Henson said the state’s analysis is based on assumptions that more electric vehicles will be traveling the highways in the future, and that the number of vehicles will increase as population does.

On Tuesday, Hogan continued to promote the toll lanes proposal during a speech to business leaders. He touted the proposal as “the largest traffic relief project in the world” and said that other politicians “have done absolutely nothing for decades” to address congestion.

“Unbelievably, some legislators and local officials are apparently in favor of continued traffic congestion and are once again working to stall our plans to solve the traffic congestion crisis,” Hogan told members of Maryland Business for Responsive Government, a pro-business group that is rebranding itself as the Maryland Free Enterprise Foundation.

It’s unclear whether the Board of Public Works will move the project forward. Neither Comptroller Peter Franchot nor Treasurer Nancy Kopp, the other two members, has said how they will vote on the project, both of them saying they have questions and are still weighing the plan.

Batterman’s message went to the offices of both Franchot and Kopp.

Opponents meanwhile continue to criticize the highway expansion and push the Hogan administration to consider alternatives. That is in part because the project would require a few dozen homes and a handful of businesses to be demolished, despite earlier assurances that wouldn’t be necessary.

On Monday, a slew of local officials and state lawmakers gathered at a park in Silver Spring to propose a multipronged approach: widening the American Legion Bridge over the Potomac River, allowing the use of shoulders during rush hour, installing lanes that can reverse traffic flow during different times of day, improving the MARC commuter train service and encouraging drivers to use the Intercounty Connector instead of the Capital Beltway.

Some also suggested investigating the feasibility of a monorail line along Interstate 270 that a developer has proposed.

Opponents of the toll lanes proposal plan to continue to push their cause Wednesday morning before the Board of Public Works vote. Local officials and representatives from environmental and transit advocacy organizations say they plan gather outside the Comptroller’s Office in Annapolis with signs and banners.