Top engineer Ted Zoli says the era of shared-use structures has arrived.
A decade ago, it was unusual to design a bridge with space for pedestrians or cyclists, says Ted Zoli, National Bridge Chief Engineer for the architecture and civil engineering firm HNTB. Today it's unusual not
to give these modes space—or, in some cases, the entire structure. Even
bridges that seem primarily suited for vehicle traffic must include
what Zoli calls, in the parlance of engineers, "shared-use path
facilities"; the new Tappan Zee Bridge will have one, he points out, as will a bridge HNTB is designing on I-95.
Zoli describes a pedestrian bridge as "fundamentally a different
facility" than a vehicular one. Oddly enough, the distinction has little
to do with the weight each must bear; that's generally the same in both
cases, he says. Rather, the difference comes down to three design
approaches: connectivity (how to get people up and down), aspiration
(pedestrian bridges should be iconic, wayfinding landmarks unto
themselves), and curvature (there's far less need for straightness).
The experience of curvature drives the majesty of the Bob Kerrey Pedestrian Bridge,
a 3,000-foot, S-shaped structure for walkers and cyclists that snakes
between Omaha, Nebraska, and Council Bluffs, Iowa, over the Missouri
River. The challenge here was finding a way to introduce curvature
without blowing the budget out of the water (so to speak). Zoli met the
task by using railing with no frills instead of a flashy finish, and
engineering structural pieces that appear curved from afar but are
actually straight at the individual level.
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