HOUGHTON — A successful piece of civil engineering can largely fade into the background.

Endlessly reproduced and photographed, the Portage Lake Lift Bridge has sidestepped that fate better than most. But most of the people crossing it — as more than 20,000 vehicles do each day — probably don’t realize how innovative it was.

The civil engineers do. The bridge was honored as a National Historic Civil Engineering Landmark by the American Society of Civil Engineers during a ceremony at Bridgeview Park Friday.

“This is an engineering marvel, and I think we should celebrate it accordingly,” said Paul Ajegba, director of the Michigan Department of Transportation.

Plaques recognizing the landmark will be put up on both the Houghton and Hancock sides of the bridges.

The recognition was spearheaded by two Michigan Technological University graduate students, Emma Beachy and Michael Prast. Their professor, Tess Ahlborn, mentioned her work in obtaining the same award for the Mackinac Bridge. In an offhand remark, she mentioned the Portage Lake Lift Bridge also qualified.

They jumped at the chance to work on it as a graduate project; Ahlborn was equally gung-ho about being adviser.

“It’s a local landmark,” Beachy said. “It’s the thing that connects the two cities, and it’s just really visually striking. And so to be able to delve more into the history of it, what went into making it, was really special.”

The bridge is the only place vehicles can cross between the Keweenaw Peninsula and the rest of the country.

It had forerunners: a floating bridge, followed by a wood bridge and swing bridge. But it’s already the longest-lasting crossing between the two cities.

The mining-era bridge was built as a double-deck bridge to accommodate rail traffic. And a sign of how the area’s economy has shifted, the lower deck now handles snowmobile traffic in the winter, and can also handle high-load vehicles.

“The engineers marveled at the bridge, which in a rarity for lift bridges, was built with an intermediate level. That has reduced the number of lifts required by 63%,” said Al Anderson, engineer with the MDOT Transportation Service Center in Ishpeming.

“These guys were really thinking when they built this bridge, to put those intermediate sets in there, so that they could get this up and get the majority of the boat traffic underneath without having to move the bridge,” he said.

Putting the 260-foot span in place was its own feat of ingenuity. It was floated into place with only 4 inches of clearance. Barges were filled with water to weigh the span down, Anderson said. Water was then let out of the barges to bring the span up to where it could be connected to the lift cables.

“Then they pumped water back in the barges in order to sink the lift span down in order to put pressure on the cables to lift the counterweights off the hangers that were in the towers,” he said.

Those counterweights, fine-tuned to within about 2,000 pounds of the 4.584-million pound span, enable a rare feature. If necessary, workers can grab a pipe wrench or a strap wrench and move the bridge by hand.

“It’s kind of a testament to the engineers, both civil and mechanical, who figured out how to make that so easy, so that you don’t need giant, powerful motors that are lifting millions of pounds,” Prast said.

To qualify for the award, a project must be at least 50 years old, possess unique features and have contributed to the development of the civil engineering profession and the nation.

The bridge handily cleared the first bar, being already close to 60 when Beachy and Prast began their work. And they documented the other two parts during their research. At the Michigan Tech Archives, they found blueprints for the bridge and read communications between officials from the 1950s over funding and various design options. They also interviewed people who loom large in its legend: Tom D’Arcy, the bridge design engineer and John Michels, one of the project engineers who oversaw construction.

D’Arcy was on hand for Friday’s ceremony, and also read a poem he’d composed to honor the bridge. He recalled the long hours that went into the design with nothing more advanced than slide rules and Monroe calculators.

“I remember that, and I have great pride to see how you folks honor the bridge, and how much the folks in this area love the bridge,” he said. “It warms my heart.”

Dennis Traux, president of the American Society of Civil Engineers, said the award is part of an effort to create more awareness of how civil engineering contributes to quality of life.

“As professionals, as a society, as a community, we’re engaged in trying to advance what it is we do,” he said. “Hopefully this landmark will help facilitate continued maintenance, continued acknowledgement, continued support for the structure that’s going to be so important for this community, for this region and arguably even for this country.”

Beachy and Prast will also give a free presentation on the history of the Portage Lake Crossing and the construction of the current bridge at 10 a.m. today at the Finnish American Heritage Center in Hancock.