Two structures in spectacular settings and out of the ordinary in concept—one completed in 2005 and the other in 2007—are being considered for the record as the highest bridge in the world, measured not in elevation but in distance above the surfaces they cross. To resolve the issue, your input is sought. Some background first.

In December 2004, when the eye-catching Millau Viaduct in Southern France opened, the French immediately claimed the highest-bridge title. They based it on the fact that the viaduct’s deck was 891 feet above the river it crossed. However, both the Royal Gorge Bridge near Canyon City, Colo., with its vertical clearance of 1,053 feet, and the Beipanjiang River Railroad Bridge near Liupanshui, China, with its clearance of 918 feet, are higher. Unfazed, the French refined their claim, touting the Millau as the highest major highway bridge—that is, the world’s highest bridge on a well-traveled motorway.

Using such criteria suggests that any lists designating the Royal Gorge as the highest bridge and the Beipanjiang as the second highest need asterisks next to their records. These asterisks would clarify that they are not on major traffic highways. If that is how it should be done, then the two newest claimants to the highest-bridge title would have to show more than one asterisk in the record books.
Who are these two come-lately record contenders? First is the Hegigio Gorge Bridge in Southern Highlands Province in Papua, New Guinea. The spider-web-looking, suspension-bridge structure, completed in late 2005, is 1,290 feet above the river it spans (nearly 240 feet more than the Royal Gorge). The second is the see-through, glass-decked Grand Canyon Skywalk, also known as the Glass SkyBridge. It opened to the public in the spring of 2007, providing brave pedestrians with spectacular views of the Colorado River Valley approximately 4,000 feet below.
Hegigio consists of a main central cable and two lower cables on each side, supporting two, deep longitudinal steel beams connected with cross beams. It has no roadway as such. One of the beams carries an oil pipeline and the other a gas pipeline, with no deck for pedestrians or vehicles. (Engineer/designer for the project was Kellogg Brown and Root.)

The U-shaped Grand Canyon walkway/bridge on the Hualapai Indian Reservation dramatically cantilevers out 70 feet from the canyon wall it ties into. Two massive, curved, parallel, structural steel beams are connected with anchor rods to the solid rock that they protrude from. The deck of the walkway, exclusively for pedestrian traffic, consists of several layers of structural "glass." The upper layer is designed to be replaced should it become marred through time and use. As with Hegigio, dealing with intense, erratic wind forces was among the major engineering concerns for the Glass SkyBridge designers. (The project’s structural engineer was Lochsa Engineering and its architect was MRJ Architects.)

Should these structures be classified as bridges? If so, should they be put in the record books as the two highest bridges in the world—Grand Canyon as number one (at 4,000 feet) and Hegigio Gorge as number two (at 1,290 feet)? And if they are so ranked, should there be asterisks next to their listings? Would the asterisks note that they are not on major highways carrying a significant number of vehicles, as the French say the Millau Viaduct does?

I personally don’t believe either structure fits any traditional definitions of a bridge, no matter how loosely interpreted. Therefore, Hegigio and the Glass SkyBridge—though extremely impressive structures—shouldn’t even be on bridge record-holder lists except maybe as footnotes. They warrant some other kind of recognition, but what?

How should these engineering marvels be recognized? Send your suggestions and comments to me at rweingardt@gostructural.com and I’ll include the best ones in a future column.

Richard Weingardt, P.E., is CEO and chairman of Richard Weingardt Consultants, Inc., a Denver-based structural engineering firm. He can be reached via e-mail at rweingardt@gostructural.com.