The shifting of the 3,400-ton span is rumored to be the biggest bridge move in history.

When moving a 1,100-foot-long bridge to a different location without taking it apart, you need a few things. There's the painfully cautious planning process, veteran work crews and heavy machinery, obviously. But you also want lots of dishwashing liquid – Dawn detergent works well, if you can rustle up a few barrels of it.

Dish soap is invaluable when it comes to sliding a 3,400-ton span from its old supports onto new ones, as engineers in Portland demonstrated this Saturday while moving the Sellwood Bridge. Over the course of 14 hours, specialists from heavy-lifting company Omega Morgan used hydraulic jacks to push the Sellwood's primary section as much as 66 feet to the side, proceeding at a glacial pace of 6 feet per hour. Unlike a certain other bridge project, this one went off without a hitch, and the slightly nudged Sellwood should reopen to traffic this week.

Multnomah County is replacing the historic truss bridge – the busiest two-lane span in Oregon – with another structure to open in 2015. Rather than disassemble it or blow it to smithereens, officials decided to keep the old bridge as a temporary "detour" over the river while workers build the new crossing right beside it. In doing so, they estimate they're saving between $5 to $10 million as well as an entire year of construction time.

The $300-million-plus operation might be a world's first for a truss span of this length. Multnomah officials say that comparisons with similar construction projects "have been difficult to find." Dan Tidwell of Portland's Image Engineering Photography, who recorded some of the videos on this page, calls it the "[b]iggest bridge move in history." And these kind of bridge transplants are likely to become more common in the future, according to Omega Morgan, as municipalities struggle to stretch every dollar of their infrastructure budgets to the max.

While this weekend's immense shifting of matter was only detectable on time-lapse video (see above and below for examples), Portlanders thronged to the Willamette River to watch it happen. As one witness put it to Oregon Live, "It's hard to describe exactly why, but this is all just incredibly exciting." How's that? Well, aside from the move itself, it could be they're excited about gaining a bridge that isn't "sort of scary to drive over," "okay if you live on the edge and expect it to collapse while you're going over it," or simply a "deathwish," according to the Sellwood's reviews on Google. (Yes, people write reviews of bridges.)

The structure is so ridden with deficiencies that it's received a federal bridge-safety rating of 2 out of 100. Counted among its failings are geologically unstable foundations, a shoulderless and medianless design that's terrible for vehicles and bikes alike, and weight constraints that prevent heavy trucks or commuter buses from crossing. Up until now, the county was literally holding the Sellwood together with plastic bandages to collect falling concrete and industrial glue.

Here's a close shot of what Multnomah has deemed the "Big Move":

Multiple viewpoints on this slick video:

A pulled-back view shows the bridge inching toward its destination in Portland's ghostly fog:

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