If you stand in the middle of the new Tilikum Crossing bridge over the Willamette River in Portland, Oregon, you may see many things whiz by: bikers , joggers, light-rail trains, streetcars, buses, even ospreys and bald eagles from a nearby wildlife refuge. You will not, however, see any cars.

The Tilikum, which took four years to construct, is the first long-span bridge in the United States to accommodate so many ways of getting from one side to the other while banning automobiles. The span follows—and shares certain characteristics with—a spate of high-profile pedestrian-bridge projects, including the Bob Kerrey Pedestrian Bridge between Omaha, Nebraska, and Council Bluffs, Iowa, completed in 2008.

Left: Construction of the Tilikum Bridge (Trimet). Right: The Bob Kerrey Pedestrian Bridge connecting Nebraska and Iowa (Mark McCabe / HNTB).

As the architects of these bridges have discovered, the absence of cars opens up new design possibilities. The Kerrey bridge, for example, has a curving, S-shaped path. The Tilikum, which was designed by Donald MacDonald, a Northern California architect who also designed the new eastern span of San Francisco’s Bay Bridge, has white cables that are angled to mimic the slopes of Mount Hood in the distance. Lacking wide automobile on-ramps, the bridge is able to fit pedestrian and bike paths on both sides (the few large car bridges that allow foot traffic have such paths on one side only). MacDonald fashioned these paths so that they jut outward at the bridge’s towers, leaving empty spaces between the paths and the main bridge. These holes create an updraft, reducing the impact of wind on walkers and bikers.

One reason for the new appeal of carless bridges is that they tend to be smaller, and thus cheaper, than major car bridges, with price tags in the millions rather than billions. The broader movement to accommodate pedestrians and bicyclists has also played a role in their rise. Notably, the few major car bridges that are being built or rebuilt nowadays—like the Bay Bridge and the new Tappan Zee Bridge, in New York—are, unlike their predecessors, providing dedicated areas for walkers and bikers. Previously, big bridges that allowed foot and bicycle traffic, such as the Golden Gate Bridge and the Brooklyn Bridge, were unusual.

A rendering of the Tappan Zee Bridge in New York City (New York State Thruway Authority)

Portland has a long history of pushing alternative transportation. When, in the 1970s, a major freeway project was scotched after public outcry, some of the funds were redirected toward one of the nation’s first light-rail lines. Later, in another widely emulated move, the city ripped out a waterfront highway and built a park in its place. And in 2001, Portland became the first American city to introduce modern streetcars.

Left: An aerial view of Riverfront in 1964 (City of Portland Archives). Right: The South Waterfront District in Portland (Craig Holmes).
Map of Portland’s light-rail-line

Like so many American cities, Portland has seen its industrial neighborhoods transition to a mix of residential and commercial use. The area west of the bridge, which in the mid-20th century was a shipyard, is now the South Waterfront district, home to towering condo buildings and the burgeoning riverfront campus of Oregon Health & Science University, one of the city’s largest employers. To the east, the Tilikum touches down in the heretofore industrial Central Eastside district, part of which is being rezoned for mixed-use development. The need to connect these changing areas was clear, and yet neither neighborhood had the road infrastructure to support the increased traffic that would have come with an additional auto bridge. Instead, the Tilikum was conceived first and foremost as a conduit for a light-rail line.

Construction on the Tilikum Bridge conduit for Portland’s light-rail line (Trimet)

Just north of the new bridge stands an older one, the Marquam, which opened in 1966 and is today one of Oregon’s most heavily trafficked bridges, carrying 135,000 cars across the river each day. With two decks and a squat frame, the older bridge makes the Tilikum seem delicate.

But don’t be fooled—a bridge full of people weighs a lot more than you might think. Semyon Treyger of HNTB, the firm that engineered the bridge, says that the Tilikum’s heaviest load will come next July 4, when it will be filled with people, packed shoulder to shoulder for the city’s fireworks display. Golden Gate Bridge authorities learned the hard way just how much a crowd can weigh during the bridge’s 50th-anniversary celebration, in 1987, when the packed span sagged about seven feet.

“If it’s crowded with people, that’s heavier than buses or trains,” MacDonald, the architect, told me. “The Tilikum is a really strong bridge.”