The Robert I. Schroder Overcrossing in Contra Costa County, California, may have set a new standard for contemporary pedestrian and bicycle bridge designs, according to an article by the San Francisco Chronicle’s urban design critic, John King. “The word ‘icon’ is used far too often in architectural hype. But at its own modest scale, Robert I. Schroeder Overcrossing shows what an icon can be,” King explained in an article. “You don’t expect to see it; once you do, you’re glad it’s there. And you look forward to seeing and experiencing it again.”
Located along the Iron Horse Trail in the major transportation and commercial hub of Pleasant Hill, the $6.8 million bridge features widely spaced cables suspended from two 42-foot-high arches that incline outward from the structure’s concrete deck. “From the street, it’s as if enormous silver bows were poised above you,” King observed. “On the deck, you move amid sculptured butterfly wings. Another twist – literally – is that the path forms an elongated “S” as it ascends from the transit village. The approach to the span threads mature oaks on one side, redwoods on the other; you angle to the west and then emerge 13 feet above the earth, the angled forms beckoning ahead.”
Noting that less-costly alternatives were considered, King credited Contra Costa’s Redevelopment Agency for finding the county, state and federal funding to build a more visually striking design. “Our society should aim to produce civic works on par with cherished landmarks from the New Deal or the Carnegie libraries of the generation before that,” King opined.
From a practical perspective, the bridge’s footprint avoids existing underground and overhead utilities that follow the Iron Horse Trail, while accommodating transit easements and established trees within its footprint. It also represents a major safety improvement for pedestrians and cyclists who use the 33-mile Iron Horse Trail, according to the San Francisco office of Arup, which served as the project’s prime engineering consultant. The general contractor for the project was Robert A. Bothman, Inc., San Jose, California.
In the project’s planning phase, Arup presented the local community with four design alternatives: steel arch, steel cable-stayed, steel truss and concrete girder. Arup reported that the steel arch design was preferred based on its cost and aesthetics. “The county officials envisioned an iconic bridge to be the centerpiece of the development of a ‘Transit Village’ around the site,” Arup project director Ignacio Barandiaran explained in an online interview.
“Aesthetics were far more important on this project than a typical industrial job,” acknowledged Tnemec coating consultant Glen Amos of Amos and Associates. “Also, keeping to a tight schedule was critical. The owner wanted disruption to the traffic flow to be kept at an absolute minimum.”
Structural steel for the 800-foot-long bridge was fabricated by Mountain States Steel in Lindon, Utah, which shop-applied protective coatings from Tnemec. All structural steel was primed with Series 90E-92 Tneme-Zinc, an inorganic, zinc-rich ethyl silicate with tenacious bonding and abrasion resistance, followed by an intermediate coat of Series 66 Hi-Build Epoxoline, a polyamide epoxy. The bridge’s steel pipe arches received a finish coat of Series 1077 Enduralume, an aliphatic acrylic polyurethane containing a sparkle aluminum pigment that creates a metallic aesthetic finish. Silver and Dark Aluminum were the colors specified.
Field touch-up and final coating application were performed under full containment by Jeffco Painting & Coating, Inc., in Vallejo, California. The applicator used Series V69F Hi-Build Epoxoline II, an advanced generation polyamidoamine epoxy, on spot repairs and iron bolts that were abrasive blast cleaned. In areas where abrasive blasting was not feasible, applicators used Series 135 Chembuild, a high-build polyamidoamine epoxy for marginally prepared rusty steel and tightly adhering old coatings. “Small spot repairs and some bolts were brushed and rolled,” noted Todd Anderson, project manager for Jeffco Painting and Coating.
Structural steel, except for the arches, received a full finish coat of Series 740 UVX, an advanced technology polyfunctional hybrid urethane that offers superior color and gloss retention and a hard, durable film that stands up to abrasion, exterior weathering and ultraviolet (UV) light. The advanced technology finish coat has less than 100 grams/litre VOC content. “For the most part, conventional spray equipment was used,” Anderson said. “The finish coat sprays nicely and can make any structure look great.”
The coating consultant and general contractor were also commended by Anderson, who observed, “Jeffco has worked with Amos and Associates for many years and they have always provided us with sound technical recommendations and service. And Robert A. Bothman understood the coating issues, as well as the aesthetics and corrosion protection that the owner was looking to achieve.”
Named for a former Contra Costa County supervisor and community activist, the Robert I. Schroder Overcrossing is the centerpiece of the Pleasant Hill Station of the Bay Area Rapid Transit District (BART) Transit Village, which is recognized as a successful demonstration of a transit-oriented development. According to San Francisco-based Urban Ecology, Inc., “With the highest concentration of multi-family housing within a quarter mile of any suburban transit hub in northern California, the Pleasant Hill BART Station shows how transit-oriented development can work. Sixty percent of those living in nearby units said BART was a major factor in moving there. Studies have consistently found that 40 percent of the area residents use BART to commute to their work place."