For nearly 50 years, ocean waves, rushing currents, hurricanes and wayward boats have hammered the Bonner Bridge. For just as long, the state Department of Transportation has struggled to keep it standing.

It's the DOT against the sea, and the price tag might soon top $100 million.

The 2.5-mile bridge rests on a bed of shifting sand in a break in North Carolina's Outer Banks. Saltwater has pocked its concrete and rusted the steel cables and bars that knit it together.

Sand has migrated from under its foundations, at one point causing it to buckle and sag.

The ceaseless contest between engineering and nature long ago earned the span a dubious title: The Bridge Most Ready for Replacement. It carries a federal rating of 2, on a scale of 100. The Mississippi River bridge that collapsed this summer in Minneapolis had a rating of 53.

State officials say that measure doesn't take into account the numerous fixes and fail-safes they have added to the bridge over the years. The DOT -- whose engineers, divers and contractors have worked under the bridge for decades -- has spent $63 million, in today's dollars, to keep the Bonner Bridge in working order. The U.S. Army Corps of Engineers spends $6.6 million a year trying to keep the channel below open for boats.

DOT engineers say that the bridge won't collapse during storms or its tourist-season peak of 61,600 vehicles per week, when it carries locals and visitors on N.C. 12 along the sliver of sand that is home to the Cape Hatteras Lighthouse and the Pea Island National Wildlife Refuge.

But there is work to do. The state, with no arguments from anybody, plans to spend $40 million more to keep the bridge open until 2015.

By that time, the state hopes to have built a replacement.

Until then, the battle under Bonner Bridge will continue. Ben Presgrave, a DOT diver, will continue his descents into the roiling current of Oregon Inlet. Like Spider-Man, he hugs the pilings, current to his back, moving down and up to check for corrosion and cracks, measuring to make sure key bridge supports are firmly embedded in sand.

"The current is awesome; it's so strong it'll blow you right across the bottom," Presgrave says. "It's nature, it's alive, it's always moving and never sits."

Underwater tug of war

On a recent bright Indian summer day, families fished off the beach in the shade of the bridge's spans. Small boats dotted the water, lines trailing into the water in search of bites. Cars and trucks whizzed by overhead, their wheels rhythmically thumping at every expansion joint.

The scene beneath the bridge is not so pretty. Saltwater has eroded the concrete. Rusted braids of reinforcing cables dangle from the belly of the roadbed. Patches of rusted rebar dot the bridge's bottom like the crude scars of Frankenstein's monster.

The rippling water hid the hydraulic tug of war under the surface. Oregon Inlet has more high winds, strong tides, storms and shifting sands than any other inlet on the East Coast. The ebb and flow is titanic on a daily basis. Hurricanes and nor'easters can blast mountains of seawater and sand through the narrow inlet and into the vast reaches of the Albemarle and Pamlico sounds.

In 1846, a major hurricane tore open Oregon Inlet, two miles north of its current location. Two lighthouses were built in the 1800s on Hatteras Island, on the south side of the inlet, and toppled into the ocean. The third, current lighthouse was built in 1872 out of harm's way on Bodie Island, on the north side of the inlet.

Accessible only by boat, Hatteras Island remained remote and largely undeveloped until construction began on the Bonner Bridge in 1962. The battle with the ocean started immediately, when a major nor'easter known as the Ash Wednesday storm wiped out the first stage of construction.

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