Garner, N.C. — Federal law is keeping the state from eliminating two of several routes as potential paths for an extension of N.C. Highway 540 in southeastern Wake County.

Steve Dewitt, chief engineer for the North Carolina Turnpike Authority, said Thursday that the so-called red and pink routes could not be taken off the table yet because of an endangered species of mussels that was discovered in a creek along the original planned expansion area – the orange route.

The Turnpike Authority said in November it was recommending that the red route, which runs through Garner, not be used because of the adverse affect it would have on 13 neighborhoods, a church and the town’s primary industrial recruitment area.

“We do not ever expect to build the route,” Dewitt said. “We don’t support it because of the huge human impacts that it does provide. But we’ve got to go through a process, and we have to follow the fed law that dictates that we do what we do and that’s pretty much the bottom line.

Dewitt said planners will begin on Friday working with the town to find alternate routes.

The orange route wouldn’t have as much of an effect on homes and businesses, but it would go through streams where the dwarf wedge mussel live.

The southeast extension of N.C. 540 will extend the Triangle Expressway – currently under construction in southeast Wake County and part of northeast Johnston County – and complete the 540 loop around Raleigh.

The Turnpike Authority expects to decide on a route by mid-2012, though the ultimate decision won't be made until the end of 2013.

Construction could begin as early as 2018.