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When the Sellwood Bridge opened in 1925, it was Portland’s first to serve only motor vehicles and not streetcars. Now, concrete will soon be poured twice as thick in parts of the new Sellwood Bridge to ensure that it’s 鈥渟treetcar ready鈥� should that infrastructure ever be called for.

The $317 million new bridge is now about 80 percent complete, with about one year of work remaining. It’s the costliest project in Multnomah County history, and much of the heavy work is already done, county spokesman Mike Pullen said on a site walk-through last week.

The old bridge is being used to detour traffic, though it stands on temporary piers after being moved 66 feet north during construction. But no more traffic closures will take place in 2015, Pullen said.

Between 150 and 200 workers with various firms are at the site most days. Lately, many have been preparing the rebar mats ahead of 10 sections of concrete pouring. A Terex bid-well machine sits poised over the width of the bridge deck, ready to set the crown of the road so that water drains downhill and toward the shoulders.

A dog park and other amenities have been built to offset environmental impacts. This week, traffic signals will go in, but won’t be turned on until next year. The project also includes bank stabilization on the west side of the Willamette River, off of Macadam Avenue (Oregon Route 43).

鈥淲e started with a broken bridge, and the project’s grown to include about a half-mile of state highway,鈥� Pullen said.

Construction challenges have included scheduling work around needs of a species of migratory fish, and securing property from five homeowners. But perhaps the biggest difficulty has involved managing traffic on the heavily-used crossing, Pullen said; approximately 30,000 motor vehicles cross it each weekday.

鈥淚t’s always a challenge to construct a new bridge while keeping traffic moving,鈥� he said. 鈥淲e’ve been shifting traffic around a lot.鈥�

Before the first bridge was built, a real estate company in 1882 began offering a free ferry to the burgeoning Sellwood neighborhood to attract potential buyers. Twenty-one years later the Sellwood City Council approved funding the John F. Caples ferry off of Spokane Street, near where the bridge stands today. (Both of the old landings can still be seen from the bridge.)

In the early 1920s, following a sordid development phase highlighted by scandal 鈥� detailed on the bridge project’s website, sellwoodbridge.org 鈥� Multnomah County commissioners selected famous bridge builder Gustav Lindenthal to design the crossing. He chose an unusual design 鈥� a steel, four-span, continuous riveted Warren Deck truss with verticals, making it the city’s first high bridge without a movable span and the only one of its kind in Oregon.

Built with pieces of the old Burnside Bridge, the Sellwood Bridge also was the first in Portland without trolley tracks, and thus had a lighter weight load. Over time, buses and trucks weighing more than 10 tons taxed the bridge, causing concrete girders to crack and railings to sag. Plastic netting now covers the damage in places, though such patches have ceased because of construction.

Other problems were still evident this month. The bridge has only one four-foot-wide sidewalk for pedestrians and bicyclists, and neither shoulders nor a median.

Conceptual work for the new Sellwood Bridge began in 2006, and construction started in 2012. It will be 64 feet wide at its narrowest, with two 12-foot-wide travel lanes, two 12-foot-wide shared-use sidewalks and two 6.5-foot-wide bike lanes. Sculptures will adorn concrete piers along the travel lanes of Tacoma Street between Southeast 6th Avenue and Southeast Grand Avenue. The general contractor is a joint venture of Slayden Construction of Stayton and Sundt Construction of Tempe, Ariz. It was designed by T.Y. Lin International.

Though thousands of drivers have been affected by the road closures, they have received appreciation from nearby residents, Pullen said.

鈥淭hey said (the road closures were) kind of nice,鈥� he said. 鈥淟ike it was their own private village.鈥�