EVERETT — The last of 251 overpass girders is set to be dropped into place on I-5 in Everett tonight, marking one of the last steps before a new, wider freeway opens.

“It’s a milestone,” said Mike Cotten, project director for the state Department of Transportation’s Everett I-5 widening project. “We’re now 90 percent complete. The light is at the end of the tunnel, and we can see it.”

With the last girder installed, the state will have built five new spans and widened 18 others between Highway 526 and the Snohomish River.

The girders, prefabricated concrete or steel spans that support highway bridges, together weigh about 24 million pounds. That’s about as heavy as 108 Boeing 787-3 airplanes.

Some girders hold up the Broadway flyover ramp, perhaps the signature element in the $263 million I-5 widening project, Cotten said. Others were used for less glamorous projects, including widening the trestlelike spans that carry I-5 through north Everett.

When finished, perhaps in March, the I-5 widening project will extend the carpool lanes that now end at the Boeing Freeway north to the Snohomish River. New merging lanes will open between 41st Street SE and U.S. 2.

The project also includes a new 41st Street SE overpass, a left-hand carpool exit from both directions of I-5 to Broadway and much-improved ramps from I-5 to U.S. 2.

The $263 million contract, paid for by a 2003 5-cent-a- gallon gas tax increase, is the third most expensive ever signed by the transportation department, behind only the new Tacoma Narrows bridge and the Hood Canal bridge.

The state had hoped to finish by the end of the year, but weather problems and equipment supply shortages have caused the finish date to slip to March or beyond.

Plans for at least opening the northbound carpool lane by the end of the year also were pushed back.

Still, drivers frustrated by two years of shifting lanes, rough roads and lane closures may be appeased by knowing that the work originally was going to take three years and not start until 2009. Thanks to a sped-up construction schedule, construction started in Sept. 2005.

Even though the end is near, work hasn’t slowed at all on site, with contractors rushing to get work done every night when the rain lets up.

The last six girders were expected to bolted into place Thursday night and tonight. They are part of a new southbound I-5 overpass over the old left-hand exit to Broadway, said Patty Michaud, a Transportation spokeswoman.

“The last girder means you’re coming up on the end of everything,” said Dave Doles, project manager for contractor Atkinson-CH2M Hill. “The last concrete pour, the last ton of asphalt, the last piece of barrier, the last fence post and the last pavement stripe. Then we’re out of there.”

Still, he cautioned drivers not to get too excited.

“We’re still not done yet,” Doles said. “We’ve still got two months of hard pushing left to do.”

Reporter Lukas Velush: 425-339-3449 or lvelush@heraldnet.com.

By the numbers

5: New overpasses

18: Widened spans

251: Number of bridge girders

24 million: Weight of the girders in pounds

153 million: Amount of rainwater, in gallons, that falls onto I-5 in the project area each year

61,000: Cubic yards of concrete poured by crews

80,000: Tons of asphalt laid down

293,068: Tons of soil, rocks and other material for roadway embankments imported and placed