Hundreds of thousands of vehicles cross The George Washington Bridge every day, making it the busiest bridge in the world.

But the 592 thick, steel ropes that help to support the roadway are aging. They have not been replaced since the bridge opened 87 years ago.

Now the Port Authority finally is undertaking that work, part of a decade-long, nearly $2 billion project to keep the landmark double-decker span structurally sound.

"As engineering professionals, we always strive to build things that are going to last way longer than our lifetime, so that our children and grandchildren can use them,” said Amanda Rogers, the agency's senior engineer of construction. “And that's what we're trying to do here."

On Wednesday, NY1 climbed hundreds of feet above the Hudson River to get a better appreciation of what these workers are doing, replacing the steel ropes as traffic rumbles along below.

"This is a tremendously complex and challenging project in how the work has to be staged,” says Port Authority Deputy Director Roger Prince. "We rely upon a significant number of very talented engineers and planners to figure out how to coordinate all this work."

Workers, many tethered to the bridge with safety harnesses, operate on a closed bike and pedestrian path, and on sloping scaffolding high above it, using a crane to cut and replace the ropes one at a time.

"We do a lot of temporary support of the structure before we remove the old rope and then we replace it with the new rope,” Rogers says. “Then we move the temporary support, and move on to the next rope, and repeat that for 592 times."

The workers say replacing the job requires nerves of steel.

"You either can do it or you can't,” Rogers says. “A lot of people don’t realize, you don't know if you’re afraid of heights until you're up here. And once you're up here, you'll know whether you are or aren't."

The rope replacement portion of the “Restoring the George” project is set to run through 2025.