“Fragile” is an adjective that gets used a lot when describing the Outer Banks, the chain of barrier islands along the coast of North Carolina. The narrow islands' ecologically sensitive dunes and marshes are home to a wide range of bird, fish, and plant species that have somehow managed to survive centuries of storms, and the more contemporary challenge of co-existence with tourists and the development impacts that inevitably accompany them.

South of the built-up areas of Kitty Hawk and Kill Devil Hills, fragile becomes an apt way to characterize the Outer Banks' transportation network—a single two-lane highway, State Route 12, and its keystone, the Herbert C. Bonner Bridge over Oregon Inlet.

Built in 1963, the 2.5-mile long, 260-span bridge carries as many as 10,000 vehicles a day 65 feet above the famous hurricane-formed inlet. What motorists don't see is a host of structural and capacity issues that earned the bridge a sufficiency rating of two in a 2006 structural assessment. The effects of time and nature are readily apparent on the structure's concrete and steel elements, while new supports on the south end have been added to combat extensive erosion of the original pilings. 

Equally as worrisome is the risk of stranded vacationers and year-round residents of Hatteras Island should something happen to the bridge, as was the case in 1990 when a runaway barge collided with the structure and knocked out a 300-foot section that took several weeks to be replaced.  Residents might be able to put up with the inconvenience of ferries for a short time but lost visitor revenue—the bulk of the Outer Banks' limited economy—might never be recovered.

A plan is in the works to replace the Bonner Bridge with a new, wider structure under a design-build contract that is scheduled to be let in early 2010. Approximately $40 million in repairs will keep the current bridge safe and in service until the new structure is completed in 2015, if all goes according to schedule.

Replacing the bridge will likely prove to be the easy part of a project that could cost $1.4 billion or more. The North Carolina Department of Transportation (NCDOT) must also contend with accelerated beach erosion at several points along Route 12, the result of a series of major storms over the past several years and, at least in the opinion of many experts, the islands' migration toward the mainland. The erosion problems could become more critical—and more expensive to address—if storm activity increases in either frequency or intensity (or both), and if climate change raises sea levels rise by even a minuscule amount in the coming years.

And that's on top of the ongoing debate about how best to preserve the federally protected wildlife refuge that forms the Route 12 corridor, and the Outer Banks as a whole. Some have called for allowing nature to take its unfettered course with the wild beaches  and limiting development in the existing areas while others assert that the challenge is nothing that some additional sand and other coastal engineering measures can't fix.

Although the project's Environmental Impact Statement, published last fall, called for elevating Route 12 at several locations, an NCDOT-led interagency panel agreed last week to explore two other options: bypassing a particularly troublesome portion of Route 12 north of the village of Rodanthe, and preserving the existing alignment through the use of beach nourishment and dune construction measures.

Each option has its trade-offs, and NCDOT faces the challenge of balancing the impacts on  beaches and wildlife areas with the need for reliable mobility. The agency plans to announce its choice when the Record of Decision is issued in October.

Meanwhile, as tourists  once again make their way onto the Outer Banks for another summer of sun and recreation, Route 12 and the Bonner Bridge hold on, two tenuous links that may prove far less resilient than the fragile environment they occupy.