Modeling the Vista Avenue Viaduct

Background

Perhaps Portland’s least well-known major bridge, the ornate and classically styled Vista Avenue Viaduct spans Tanner Creek Canyon in the Goose Hollow neighborhood, connecting King’s Heights with Vista Ridge. Crossing high above Canyon Road in a now quiet corner of downtown, the location was once the primary connection used to cross the West Hills and a gateway for farmers in the Tualatin Valley who needed access to Portland harbors.

Finished in 1926, the Vista replaced the 1903 Ford Street Bridge which was built to carry streetcars to the Lewis and Clark Exposition’s "Big Tree Observatory" atop Council Crest. After the Exposition, the bridge continued to carry riders to the growing neighborhoods in the West Hills and to the Council Crest Amusement Park which opened in 1907. The popular park was conceived by the Portland Railway Light and Power Company as a way to attract riders to the new Portland Heights streetcar line. Until it closed in 1927, the park featured a dance hall, ferris wheel, merry-go-round, miniature railway and sternwheeler, and canal boat rides.

The Ford Street Bridge was a narrow, noisy, timber-plank structure that irritated nearby residents. As a replacement, the Portland Heights neighborhood “sought an aesthetically pleasing structure unlike any other in the immediate urban area” and the Vista Bridge’s uniquely decorated design was made possible because half of the $197,000.32 price was paid for by the wealthy neighborhood.

Vista Avenue Viaduct roadway with streetcar tracks and power lines in 1927. Image identified by Vintage Portland. (City of Portland Archives, Oregon, A2009-009.2202.)
Vista Bridge from Washington Park in 1935. Image identified by Vintage Portland. (City of Portland Archives.)

Citing its significance to Portland as “a delicately engineered inter-city structure which has played a vital part in the city's transportation network”, the bridge was added to the National Register of Historic Places on April 26, 1984.

Despite the optimistic spirit surrounding the bridge’s construction, it would soon gain notoriety as Portland’s “Suicide Bridge”. The Oregonian newspaper reported the first suicide on the bridge five years after the bridge opened, and in subsequent decades, the bridge would regularly see more suicides each year than all other Portland bridges combined. In 2013, after three suicides in six months, a temporary fence was added by emergency order, citing "a substantial threat to the welfare and safety of the public above and below the bridge."

Ten years later, the temporary fence remains in place, blocking access to the bridge’s low railings and seating areas. Although there have been various objections to the impacted views and the trash that collects behind the fence, there have been no successful jumps since the fence was installed.

Vista Avenue Viaduct from below, facing southwest. (Photo: Kalin Schmoldt, 2023.)
Vista Avenue Viaduct with security fence, facing northwest. (Photo: Kalin Schmoldt, 2023.)

Designed to last at least 50 years, the bridge is now approaching its 100th birthday. Although it no longer carries streetcars to Council Crest, and most travelers now use the Vista Ridge tunnels instead of Canyon Road, the bridge still serves as a gateway, framing beneath its central arch the light rail tunnel that provides public transit access to Washington Park.

Design and Construction

Vista Avenue Viaduct under construction in 1926 with visible falsework and active streetcar line. Image found at Vintage Portland. (City of Portland (OR) Archives, AP/27003.)

The Vista Bridge was designed by City of Portland Bridge Engineer Fred T. Fowler. It is considered a viaduct because it is relatively level and connects two hills across a canyon.

The structure is a rib-reinforced open spandrel concrete deck arch, 549 feet long between abutments, with a 248-foot central span. The classical arch style was popular in the 1920s and 30s and the bridge supports are detailed to resemble classical columns, with stylized bases and capitals.

Although relatively small compared to other major Portland bridges, Vista’s short span holds a wealth of pedestrian level design details, including: an ornamental railing, precast stone light posts topped with bronze lanterns, refuge bays with stone seating, curved sidewalk entrances with planter gardens, and art-deco inspired entrance pylons topped by cut copper and tinted glass lanterns.

Vista Avenue Viaduct Refuge Bays.
Roadway and end gardens.

Although classical symmetry is apparent throughout the bridge design, the bridge has perplexingly irregular girder spacing on the underside. This was due to the requirement that the streetcar line had to remain in operation throughout construction. To facilitate this, the bridge was built around a separated rail trestle. The separate structure was necessary in order to prevent vibrations from the trolley from impacting the concrete setting process. Streetcars continued to cross the Vista Bridge until 1950, when service on the Council Crest line and Portland’s other remaining streetcar lines was abandoned. The unused streetcar tracks and trolley wire poles remained on the bridge until the bridge deck was replaced in the 1980s.

Vista Avenue Viaduct piers, arches, and girders from below.
Vista Avenue Viaduct under construction with active streetcar line. (Image cropped and enhanced. Courtesy of the Lake Oswego Public Library.)

Modeling Process

SketchUp is (ostensibly) a simple program that is about connecting points in space to other points in space to create more complex shapes. However, as someone mostly familiar with using SketchUp for small, measurable projects, the bridge project forced me to grapple with two fairly obvious challenges: identifying just where to put those lines based on limited information, and how to efficiently manage and organize the many design elements that would become necessary for the model.

In contrast to Portland’s steel bridges which use hundreds of geometrically oriented girders, the concrete Vista Bridge’s main structure is a relatively monolithic assembly of solid looking (but actually hollow) piers, abutments, arches, and columns. In the absence of technical drawings, the bulk of the structural modeling was fairly simple given available photographs, written descriptions of the bridge features, and a few measurements taken onsite with a tape measure.

The process was complicated by the fact that much of the structure outside of the main span is tucked into the hillside, obscured by trees, covered with ivy, and unreachable because of security fences. Measurable aerial photographs and topographic data provided rough dimensions, but these were imprecise. Determining the relative sizes and locations of these massive elements required numerous, iterative adjustments whenever it became apparent that my components would not fit alongside their known counterparts.

Modeling the light posts and railings was somewhat simplified by the discovery of a few design drawings, but even for those elements, and for the rest of the model, the challenge of how to efficiently organize all the pieces remained.

Vista Avenue Viaduct structure.
Vista railing, pylon, and garden detail study.
Working half-model showing canyon elevation profile and notes.

Becoming disciplined at grouping and labeling was essential, as was learning the most efficient techniques for avoiding unnecessary work. One essential strategy involved reducing the bridge to its most essential parts and then identifying symmetry in what remained so that individual components could be created once, then copied, scaled, and rotated to fill out the rest of the model. Recognizing opportunities for this kind of efficiency required a new way of thinking, and it was made more difficult by the bridge’s propensity for subtle asymmetry. Upon close inspection, Fowler’s Vista Bridge alternates the size and shape of various pedestals, the height of lamp posts, the spacing of girders between spans, and includes four unique, curving garden areas that fit into the distinct topography at each bridge corner.

The art of identifying repeatable components also taught me important lessons about optimizing a model both for computer system performance and the best use of design time. It simply wasn’t necessary or worth the loading time to use perfect, smooth, complex curves when simpler shapes would do.

Keeping the end user perspective in mind was another critical lesson in efficiency, and a less-is-more perspective also applied to deciding which bridge features should be included at all, or how detailed the details should be. However, while I agree that it is not usually worth the effort to model details that someone will never see, it was difficult to let some details go. It seemed perfectly consistent with the spirit of this particular bridge to include absolutely everything; even the original builders included design elements that they knew could only be appreciated with binoculars or by the birds roosting in its girders.

Vista Bridge Garden and Light Post Detail Rendering

Light post, pylon with dedication plaque, and end-garden.

Presentation Notes

I visited the Vista Bridge on a cold, wet December day, and the experience struck me in much the same way that the Witch’s Castle in Macleay Park always excited me when I was growing up in Portland. Here I’d found an unexpected, mysterious stone relic in an otherwise young city, something from Colin Meloy’s Wildwood perhaps … a secret tucked away amongst ancient trees, best discovered on foot while exploring the numerous paths in the West Hills.

Vista Bridge end-garden. (Photo: Kalin Schmoldt.)

Based on that experience, I took a few liberties with this model in defiance of reality. I opted to focus on the natural surroundings and to omit nearby buildings, powerlines, and tent camps, though I kept the light rail in homage to the streetcars that were so much a part of the bridge’s original purpose. To improve the view, I’ve pruned back the trees and pulled down the ivy obscuring the bridge piers. I’ve also restored the appearance of the now broken lanterns, removed the chainlink fence, and scrubbed away the graffiti and handwritten “Suicide Bridge” from the bronze signage.

Still, in recognition of the bridge’s complex history, I want to close with two contrasting perspectives:

The view to the east is best on a clear day when you can see Mount Hood peeking over the downtown skyline. The title shot for the show Portlandia was filmed here before the fence was added - a show that itself recalls happier times for downtown Portland.

Vista Avenue Viaduct, looking east towards downtown and Mt. Hood.

In contrast, I think the view to the west is best in the winter, in the rain, when naked trees afford views of the structure, when the moss is at its most green, and misty, cloudy days stir the imagination.