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% 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.

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.

Baltimore Sun reporters Pamela Wood and Christine Condon contributed to this article.