The Supreme Court has unshackled federal agencies from seemingly endless and time-consuming environmental reviews long demanded by activists attempting to block public works projects from being built.

The ruling, released Thursday, came in a case involving a long unbuilt rail project in Utah, but it will limit the scope of reviews on many other projects across America.

In an 8-0 ruling, the justices said the National Environmental Policy Act, also known as NEPA and signed by President Nixon in 1970, has been misused as a “blunt and haphazard tool” to unnecessarily stop, or at least slow down, new projects.

The federal Surface Transportation Board approved the proposed 88-mile Utah railroad project in 2021 after producing a more than 3,600-page environmental analysis. Environmental groups sued anyway, claiming the voluminous report had not taken every possible future impact into consideration.

The U.S. Court of Appeals for the District of Columbia Circuit ruled against the project, saying it had not sufficiently considered the environmental effects of projects separate from the railroad line itself. The Supreme Court overturned that decision, saying reviews only need to consider the project in question.

Writing for the majority, Associate Justice Brett Kavanaugh said, “Simply stated, NEPA is a procedural cross-check, not a substantive roadblock. The goal of the law is to inform agency decisionmaking, not to paralyze it.” He went on to write that the courts should defer to regulators over “where to draw the line” on impact studies.

The Republican governor of Utah, Spencer Cox, was among many conservative officials celebrating Thursday’s decision. “The court unanimously stopped an insane idea that doesn’t exist anywhere in the law,” Mr. Cox posted on X. “Extreme leftist groups have been destroying our ability to do anything in this country and weaponizing what was once simple and straight-forward.”

Senator Curtis, Utah’s junior senator, also called it welcome news. “For too long, litigious groups have weaponized environmental reviews to stall critical projects — oil, gas, wind, solar, nuclear, and more,” Mr. Curtis said on X.

The Trump administration has vowed to speed up infrastructure projects around the country. The Federal Communications Commission’s chairman, Brendan Carr, said the decision will help with priorities that “have been held back by reams of red tape.” He said “environmental hoops” have now been eliminated.

One of the groups involved with the suit reacted with concern. “Today’s decision undermines decades of legal precedent that told federal agencies to look before they leap when approving projects that could harm communities and the environment,” Earthjustice’s senior vice president, Sam Sankar, said in a statement.

“The Trump administration will treat this decision as an invitation to ignore environmental concerns as it tries to promote fossil fuels, kill off renewable energy, and destroy sensible pollution regulations,” Mr. Sankar said.

Four other conservative justices joined Justice Kavanaugh in his opinion. Justice Sotomayor wrote a concurring opinion that was joined by Justice Elena Kagan and Justice Ketanji Brown Jackson that used a narrower legal reasoning to support the decision.

Justice Neil Gorsuch recused himself from the case without giving a reason, but the Associated Press said he had faced calls to step aside over ties to a Colorado billionaire who owns oil wells in the area of the railroad project, who could benefit from its completion.