Millions of tax dollars are being spent to temporarily fix and then permanently repair an I-5 bridge that collapsed into the Skagit River.

But when the work’s all done, Washington will be left with exactly what it had before: A functionally obsolete, fracture-critical 58-year-old bridge that could come crashing down the next time it gets smacked hard enough in the right place.

“While it’s going to be in the same [classification of bridge], it’s going to be safe to drive on,” said Travis Phelps, a state Department of Transportation spokesman. “We’ll continue to inspect our bridges every two years to make sure they are in good shape.”

Tearing it down and building a brand spanking new bridge might be desired, but Washington can’t afford it.

That means it will retain the same rating it had on the evening of May 23 when a southbound semi-truck hauling an oversized load in the right lane struck several of the bridge’s overhead trusses, causing a 160-foot section to tumble into the river. Two vehicles went into the water, but the three occupants survived.

It’s still going to be functionally obsolete because it was not designed to handle today’s traffic volumes, Phelps said. Moreover, the trucks traveling on the bridge are taller, wider and heavier than those on the road when this four-lane bridge opened in 1955.

Washington state had 1,624 functionally obsolete bridges as of February 2009, according to a tally published by the Federal Highway Administration. Absent a complete replacement, the bridge will continue to be deemed fracture critical, which means it is one freak accident away from collapse. There are thousands of bridges in the same condition nationwide.

Phelps said it will be safe to drive on when a temporary span opens as early as this week. A permanent segment will be in place by Oct. 1.

Crews spent the weekend aligning and securing the spans and hoped to begin putting in the bridge deck today, Phelps said. The deck will need to be paved with asphalt and the lanes striped. Once it reopens, traffic will be required to drive much slower than before because the lanes will only be 11-feet wide, roughly a foot narrower than they were before.

Thus far, the federal Department of Transportation has committed $16.6 million for the two projects from its Emergency Relief Fund. The federal agency provided $1 million in the days following the collapse and then last week pledged another $15.6 million.