SAN FRANCISCO (CN) – A plan to widen a mile-long stretch of highway that hugs ancient redwoods in Northern California would turn a majestic grove into an “unrestricted industrial artery” for big trucks, environmentalists claim in a new lawsuit.

Joined by a group of individuals and nonprofits and represented by Stuart Gross of Gross & Klein in San Francisco, lead plaintiff Bess Bair on Friday fired off her third lawsuit in seven years against the California Department of Transportation, or Caltrans.

Bair says the state’s renewed effort to widen a 1.1-mile section of Highway 101 that threads through Richardson Grove State Park in Humboldt County could severely damage or destroy 1,000- to 3,000-year-old redwoods.

On May 22, Caltrans re-approved the project based on a revised environmental review that found it would impact the root zones of 109 old-growth redwoods rather than 66 estimated in the state’s original 2010 study.

“Caltrans once again is attempting to plow through a destructive and needless highway widening project that will both waste millions of public money and likely destroy one of the last remaining irreplaceable stands of ancient old-growth redwoods, without studying the severe and permanent environmental consequences,” the environmentalists claim in their 69-page complaint.

Supporters of the project say it’s necessary to make the transportation of goods more efficient. Coming from San Francisco, big rigs must take a 446-mile detour around the highway to reach Eureka near the northern tip of the state.

Caltrans spokesman Phil Frisbie said the $21 million project would only make minor adjustments to the highway so trucks that are “slightly longer” than currently allowed can traverse the road.

“No old-growth redwood trees would be removed or threatened by this project,” Frisbie said in an email Friday. “Caltrans has taken the utmost care in designing the project with sensitivity to the environment and has thoroughly analyzed potential environmental impacts.”

Frisbie said the project would disturb only 0.67 acres of soil along Highway 101, a miniscule fraction of the park’s 1,800-acre footprint.

But opponents say Caltrans merely re-validated its previous findings without conducting a thorough analysis, even though its prior conclusions were based on inaccurate data.

In April 2012, U.S. District Judge William Alsup ordered the state to produce new maps to identify, number and calculate the root zones of each ancient-growth redwood affected by the project. Alsup found the state had relied on inaccurate data when it issued a “no significant impact” finding in 2010, allowing it to bypass a full environmental review.

“Caltrans claims to have corrected the glaring errors that accompanied Caltrans’ initial 2010 approval of the Richardson Grove project,” the complaint states. “However, Caltrans has left largely unchanged the analyses and conclusions previously reached based on erroneous data, but has purposely prevented exposure of its new conclusions and claimed analyses to any public scrutiny or comment.”

Responding to complaints that the latest project approval was done without proper notice or public input, Frisbie said four public meetings and five public comment periods have been held for this project, “more than any other contemporary project in Caltrans District 1.”

Opponents also claim the state is pushing the project forward primarily to benefit “corporate giants” and the trucking industry.

The environmentalists further argue the project is unnecessary because oversized trucks can still traverse the redwood-hugging highway when accompanied by an official California Highway Patrol escort.

“Indeed, the approximately $21 million that Caltrans estimates the proposed project would cost could, using the current average salary numbers, pay the entire salary of a CHP Officer posted at the grove to escort the occasional [Surface Transportation Assistance Act] truck for 178 years,” the environmentalists contend in their lawsuit.

Established in 1922, Richardson Grove State Park is home to redwood trees thousands of years old soaring up to 300 feet high with diameters as large as 18 feet.

Opponents claim the state’s approval of the project violates the National Environmental Policy Act, Wild and Scenic Rivers Act, and Administrative Procedure Act. They seek an injunction to stop the project from going forward.

Individual plaintiffs include Bair, Trisha Lee Lotus, Jeffery Hedin, and David Spreen. Nonprofit plaintiffs include the Center for Biological Diversity, Environmental Protection Information Center, Californians for Alternatives to Toxics, and Friends of Del Norte.