Metal’s Urban Impact

If you are ever strolling along the iconic High Line of New York City, switching trains to get to Washington Dulles International Airport (IAD) in Virginia, or walking along America the Beautiful Park towards downtown Colorado Springs, you may find yourself on robust bridges that share a compelling commonality.

So, what feature do the High Line Connector in NYC, N.Y., the Park Union Bridge in Colorado Springs, Colo., and the Silver Line Rail Extension project in Virginia share? Delve into their distinct architectural designs, and you will discover a unifying element—metal.

A tale of three bridges

Each project showcases metal in its own unique way. The sleek, modern lines of the Connector’s railings to the smooth curves of the Park Union Bridge’s hybrid steel structure, and the functional yet elegant metal mesh used in the Silver Line Rail Extension project.

The High Line-Moynihan Connector, technically, a linear park made of two bridges over Dyer Avenue and West 30th Street, completes a chain of pedestrian pathways from Pennsylvania Station to Hudson Yards and the High Line to the West Village. Spanning183 m (600 ft), it offers a journey from Midtown West to the scenic High Line, blending contemporary spaces with greenery and history. Visitors can exit Moynihan Train Hall and cross Ninth Avenue into Brookfield Properties’ Manhattan West to find a 1.05 ha (2.6-acre) public plaza leading to the Timber Bridge, which runs along Dyer Avenue. After the Timber Bridge, they turn onto the tree-lined Woodland Bridge along 30th Street, which takes pedestrians to the High Line Spur. What connects these two bridges? Aesthetic unity, provided by Corten steel decking and bronze handrails to guide pedestrians.

Next, the Silver Line Rail Extension project, enveloped by metal meshing all through the structure. This bridge creates a system of connections to the IAD in Virginia through six new stations: Reston Town Center, Herndon, Ashburn, Loudoun Gateway, Innovation Center, and the IAD. The Silver Line Rail Extension is one of the largest U.S. capital construction projects, encompassing 18.3 km (11.4 miles) of new track, six Metrorail stations, and a 36.4-ha (90-acre) railyard. The project engineer and material supplier, GKD Metal Fabrics (GKD), provided more than 5,853 m² (63,000 sf) of oversized framed metal mesh panels, with engineered hardware, to clad bridge spans, stair infill, turnstiles, and curtain wall. This spans the entire length and height of pedestrian bridge sections to ensure optimal safety.

Last, Colorado’s Park Union Bridge. The 76.2-m (250-ft) curved, 300-ton (272-tonne) steel structure floats above an active railyard. Two interlocking loops, stretching from either side of the railyard, connect the U.S. Olympic and Paralympic Museum and America the Beautiful Park, made exclusively for pedestrians and cyclists. At its widest point, the bridge features openings on each side that frame the museum and downtown to the east. Below, there’s a platform for trainspotting, and to the west, a view of the Rocky Mountains. In the evenings, lights along the floating steel bridge create a sense of speed and motion as they illuminate the path for pedestrians and cyclists, tracing a single line from one side of the tracks to the other.

Bridging differences

While these bridges look nothing alike, they stand as examples of the versatility of metal in such large urban structures. The different ways metal is used in these three bridges show why it is an essential component of large-scale constructions. Beyond their metal elements, these projects are further united in their core function as pedestrian bridges, highlighting their shared emphasis on urban connectivity and accessibility.

Upon closer examination, it becomes evident how its varied uses contribute to the structural integrity of each project.

Metal railings, columns, and decking: Metal is a key element throughout the project. The Connector is supported  by exposed weathered steel columns and angled bracket arms, which adjust to the varying soil depths along the diagonal pathway. Its warm material palette of Corten steel decking coupled with bronze handrails serve as guides to pedestrians. “We used weathered and galvanized steel to solve multiple challenges at once,” says Skidmore, Owings & Merrill (SOM) principal Kim Van Holsbeke. “We created a highly durable, low maintenance structure that could be rapidly erected through prefabricated connection nodes on both the Woodland and Timber Bridges. The weathered steel also complemented the natural aesthetic of the timber and the landscaping, with a rich color that will patina over time and evoke the historical context of the neighborhood.”

Metal meshes: The 5,853 m² (63,000 sf) of large, framed metal mesh panels were used to span the Silver Line Rail Extension bridge. GKD’s engineering team worked closely with the architects to integrate attachment solutions that account for wind, snow, and live load considerations. They selected two weaves, Ellipse 2 and Ellipse 14, which have horizontal patterns with stainless-steel mesh warp wires across the entire surface. “The architects envisioned a passenger environment infused with natural light and ventilation. Using metal mesh provided these required elements, plus fall protection and visual interest,” says Tom Bialk, GKD-USA, vice-president of engineering. The Silver Line Rail Extension, one of the largest U.S. capital construction projects, opened in 2022.

Metal shell: The architecture of the Park Union Bridge draws inspiration from the graceful, gravity-defying movements of athletes. This bridge ingeniously combines truss and arch forms into a curved hybrid steel structure, paying homage to the U.S. Olympic and Paralympic Museum (also designed by Diller Scofidio + Renfro),  while serving as a landmark that offers visuals and pedestrian access to important areas in downtown Colorado Springs.

The curved steel structure appears to float. The shell of the bridge is painted structural steel, the liner painted metal panels, the deck is built in concrete, while the elevator that takes pedestrians to the top features glass. Stainless steel cable mesh and a comfort railing made with the same material with integrated lighting offer fall protection. “The Park Union Bridge is an exercise in fitness—both in terms of material and geometry. The hybrid steel structure system functions as an arch and a truss. Building the svelte profile across an active rail line posed complexities to the construction process. Using steel, the team was able to prefabricate bridge sections off-site and weld them together section by section. Since the bridge had to be installed with minimal  disruption to national freight train traffic, it was driven fully assembled to the side of the tracks by self-propelled modular transporters and attached to its abutments in a carefully orchestrated process that was completed within an eight-hour window,” says Benjamin Gilmartin, DS+R partner-in-charge and lead designer.

Safe and sound

The architects behind these bridges have carefully considered their users. What is notable is the role metal plays in providing fall protection, safety features, and overall sturdiness in various weather conditions, making them structurally sound and capable of withstanding large, constantly flowing crowds.

“The design required the mesh to span the full length and height of the pedestrian bridge sections, without compromising the safety and integrity of the infrastructure. We fabricated multiple framed panels with attachment hardware that enabled crews to pre-install the panels under tension while also accommodating movement between the bridge sections,” Bialk of GKD-USA adds.

These bridges exemplify the innovative use of metal in modern architecture, showcasing its versatility and strength in creating urban landmarks.