RALEIGH - Environmentalists want federal regulators to review whether plans to replace the aging Bonner Bridge to Hatteras Island violate federal law because they fail to address the state of the highway that crosses the bridge.

In a letter Tuesday to the federal Council on Environmental Quality, the Southern Environmental Law Center and Audubon North Carolina challenged plans to replace the aging bridge with a span built almost parallel to the existing one.

The organizations said the review board's failure to address the state of N.C. 12 will ultimately delay completion of the project.

"By ignoring the critical questions about what to do with the ever-eroding Highway 12 south of Oregon Inlet, state and federal agencies have punted on the most serious and important questions surrounding Bonner Bridge's replacement," SELC attorney Amy Pickle said in a news release.

The review board, made up of officials from transportation and environmental agencies, on Monday endorsed a plan to replace the Herbert C. Bonner Bridge, which opened in 1963 across the Oregon Inlet between Hatteras Island and Bodie Island.

The bridge has a sufficiency rating of 2, with 100 being the best. Repairs are set to start this year. State transportation officials have said the bridge is safe to cross.

The board also agreed to move forward with the next stages of the short bridge, which include improvements to N.C. 12 south of the bridge.

The cost of the combined project is estimated to be between $1.1 billion and $1.3 billion, with the cost of the 2.5-mile bridge alone estimated at between $294 million and $347 million.

The officials said that more environmental impact studies are needed before the short bridge plan gets final approval.

"The environment in the study area is complex and constantly changing. The ability to predict the effect of Mother Nature's future impact on the study area is extremely difficult to quantify," the joint statement issued by the agencies read.

"The shoreline alone is continually moving and unexpected storms will exacerbate the uncertainties. The environment present today can be changed overnight by Mother Nature," the statement continued.

The environmental groups said the first phase of the Department of Transportation plan avoids saying how and when other phases will be carried out. Those phases, the organizations said, must include a more reliable route than the existing N.C. 12 to comply with the National Environmental Policy Act.

The Council on Environmental Quality is an independent federal agency that enforces the act.

The review board identified the short bridge plan as the "least environmentally damaging practicable alternative." But the environmental groups noted that the board acknowledged that the short bridge will not provide the reliable access for daily and emergency traffic required under the environmental act.