Atlanta runway bridge being built over interstate

Building a massive, 1,500-foot bridge over one of the busiest freeways in the world is difficult enough, but imagine designing such a bridge that also has to withstand the stress of 1.2-million-pound superjets taking off and landing.

Architectural firm Heath and Lineback of Marietta, Ga., found that when designing the gigantic runway overpass for Hartsfield-Jackson International Airport in Atlanta, special consideration had to go into the design. The runway overpass and an additional taxiing bridge are both part of a 10-year, $5.4 billion airport expansion. The runway bridge, which will span Interstate 285, is expected to cost $159 million to build. The bridge will be one of the largest of its kind in the world.

All bridges vibrate, but it is especially important that the runway and taxiing bridge move as little as possible because it could affect the ability of pilots to control their aircrafts. So contractors are using a special high-strength concrete, which is 2 1/2 times stronger than concrete used in commercial construction. Combined, the runway and taxiing bridges will use approximately 106,000 cubic yards of high-strength concrete.

Another challenge will be building a portion of the runway on land. In order to get dirt for the runway’s foundation from one end of I-285 to another, contractors have constructed a giant conveyor belt that crosses the highway, bringing the dirt 5 1/2 miles to the jobsite.

Until Feb. 23, bridge construction did not affect traffic. But, as construction crews prepare to install the beams, the interstate’s 10 lanes are being closed off two lanes at a time so that no construction will take place over moving traffic. The speed limit was lowered to 55, and will likely be reduced again due to the construction.

Approximately 200 electricians, masonry workers, fire protection professionals, carpenters and other construction workers are working around the clock on the project, alternating two-12 hour shifts. Once finished, the runway bridge will seem like a 1,500-long, 70-foot-high tunnel to drivers on I-285, and planes landing and taking off won’t be visible from the road. The taxiing bridge, however, will carry slow-moving planes to the new runway, and will only be as high as traditional bridges. For drivers, large planes will seem as though they are right on top of the freeway. The bridges will not only span all 10 lanes of I-285 traffic, but will leave enough space for the freeway to expand up to 18 lanes.

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Atlanta’s fifth runway, with its new bridges, is scheduled to open in May 2006.