- Engineer: David W. McDonnold
Completed in 1982 as part of a major highway expansion, the Pennybacker Bridge is a steel through-arch bridge that extends across Lake Austin. The structure is 87 feet wide and its span is 600 feet long. The bridge is located in a scenic area of the Loop 360 Highway near a popular overlook, with views of the hill country and downtown Austin.
From the busy tourist perch above Lake Austin, the Pennybacker Bridge (also known as the 360 Bridge) forms the centerpiece of a sweeping vista containing rolling hills, Lake Austin, limestone cliffs, and the city skyline. With its delicate cables strung within a sturdy frame, the Pennybacker Bridge evokes the elegance of a finely-tuned musical instrument.
The structure is composed of two sweeping steel arches connected by horizontal Vierendeel struts. Cross bracing is limited to the underside of the road deck, keeping the visual elements of the bridge remarkably uncluttered. Suspended by 72 steel cables, the roadway is positioned between the base and peak of the arch, categorizing the Pennybacker as a through-arch bridge.
One of the key features of the bridge is that the structure does not touch the water below, leaving clear passage for boats. This minimal impact approach is thanks in part to environmental concerns voiced by the American Institute of Architects and members of the community at the time of the bridge’s design in the late 1970s. By the time it was completed in December 1982, the Pennybacker Bridge was only the second of its kind in the world.
The reddish-brown color of the weathering steel is the result of oxidation; this protective surface coating requires minimal maintenance and no painting. Although the steel of the bridge was sandblasted to accelerate an even layer of rust, the structure is not named for its penny-colored patina, but rather in honor of Percy V. Pennybacker, an early 20thcentury civil engineer notable for his innovations in welding technique and infrastructure design.
The bridge’s rusted patina and restrained form not only make the bridge feel like it belongs to the landscape, but also call attention to the structure’s striking beauty. At highway speed, traveling the bridge takes only seconds, but the passage is transfixing. Red horizontal ribs register against the sky in quick succession, creating a dynamic rhythm that briefly frames the sky and then slips away. – Claire Townley