New bridges on Interstate 10 will speed traffic across lake

Published 3:58 pm Tuesday, July 3, 2007

The two bridges — known as the twin spans — where Interstate 10 crosses Lake Pontchartrain will one day become wider, taller, and stronger — in fact, hurricane proof, if the builders are to be believed.

A line of pilings has already formed, the foundation of the largest public works project in Louisiana history: a new $803 million bridge that will be completed in about four years.

The new bridges will soar 30 feet above the lake with 80-foot-tall high-rises, tall enough to keep the spans above storm surge, officials say. The current spans are a mere 8 feet above the water, with 65-foot high-rises.

The existing bridges’ height, or lack thereof, combined with their design, allowed Katrina’s storm surge to dismantle them, said John Horn, resident engineer for Volkert Construction, which oversees the day-to-day operations of Boh Bros. Construction and Traylor-Kiewit-Massman Joint Venture. The surge knocked 437 bridge sections out of alignment and sent 58 of them tumbling to the lake bottom.

Engineers say a storm surge won’t be able to do the same to the new bridge.

Height alone won’t be the bridge’s saving grace, said Mark Lambert, spokesman for the state Department of Transportation and Development.

When the highway department designed the new bridges, Lambert said, engineers took into account the vulnerability of the design and construction techniques used for the old bridge with girders simply bolted to the caps they sit on.

The new bridges will still have girders resting atop the caps. Built into the caps will be 1-foot-thick, rebar-enforced “restraining walls” that fill in the spaces between each girder.

While reinforcing steel built into the caps connects them to the girders, the restraining walls essentially lock each span into place until the bridges’ inclines reach 30 feet, Horn said, preventing any sideways movement.

Stronger construction that can survive a beating from Mother Nature was the major goal for engineers, but they also sought to provide a wider bridge to accommodate the estimated 55,000 vehicles that will use the spans each day.

The highway department said it designed the new bridges to handle 50 percent more traffic.

The new three-lane bridges will eliminate the bottlenecking that now occurs when three lanes of I-10 traffic squeeze onto the two-lane bridges.

One of the new bridges alone will almost be as wide as both the existing bridges combined. With three driving lanes and two shoulders, each replacement bridge will be 60 feet wide. The existing twin spans are each 36 feet wide, with two lanes and one shoulder.

For now, Horn said, the main goal is to meet the initial construction contract. Progress is on schedule, he said, though it’s split between the east and west spans.