PACIFICA (CBS SF) – Hundreds gathered on a coastal San Mateo County hillside Monday to celebrate the opening of two tunnels that will replace a notorious stretch of state Highway 1 at Devil’s Slide.

The event marked the completion of the $439 million Tom Lantos Tunnels, which bypass a steep, winding portion of coastal highway between Pacifica and Half Moon Bay that has long been susceptible to rockslide-related closures.

READ MORE: California Reopens: Newsom Marks End of COVID Restrictions, Awards $1.5M to 10 Vaccine Recipients

On Monday morning, under gray skies, a crowd gathered outside the tunnels, named after the late U.S. Rep. Tom Lantos, whose former Congressional seat is now filled by Jackie Speier.

Addressing the crowd, state Sen. Jerry Hill said that one of the most devastating landslides along Devil’s Slide forced a closure of Highway 1 that lasted for several months in 1995.

The closure turned Pacifica into “the world’s biggest cul-de-sac” and generated momentum to find a permanent solution to traveling safely and securely through the area all year round.

Caltrans had initially proposed an overland by-pass route east of the troubled roadway, a proposal that met with fierce opposition from local citizens who were concerned about the impact of constructing a four-lane highway over Montara Mountain.

Pro-tunnel advocates—who eventually called themselves “tunnelistas”—worked tirelessly to bring the issue to San Mateo County voters, who in 1996 passed Measure T and launched the planning process for what would become the state’s newest tunnel to be built since Oakland’s Caldecott Tunnel in 1964.

Several dozen “tunnelistas” attended Wednesday’s ribbon-cutting, many carrying yellow bumper stickers from the Measure T campaign that read “Think Tunnel.”

Moss Beach resident Zoe Kersteen-Tucker stood before the northbound tunnel bore and thanked the pro-tunnel advocates, who she called “rabble rousers, activists and crusaders.”

“Hooray! It’s the ‘people’s tunnel,’” she said. “We did it!”

Speier, who called the tunnels “a new landmark” and “the Golden Gate Bridge of the south,” acknowledged the dedication of lawmakers and county residents who helped make the tunnel project a reality.

READ MORE: Breed: Free Rides As San Francisco Cable Cars Return In August For Test Runs

“Tunnel vision is sometimes the broadest vision of them all,” she said.

Lantos’ widow Annette Lantos fought back tears as she recalled her late husband’s efforts to get the massive infrastructure project started.

“It’s very sad to be here without my husband,” she said. “I just hope that, from some perspective, he’s watching us.”

“He would be so happy to know that it bears his name,” she said.

The ceremony concluded with a parade through the southbound bore that was led by the Half Moon Bay High School marching band playing “California Here I Come.”

The band was followed by a caravan of mostly vintage cars that included a Ford Model T, a DeLorean, a Volkswagen Vanagon and the San Mateo County Book Mobile.

Sometime between Monday night and Tuesday morning, traffic from Highway 1 will be permanently diverted into the tunnels, according to Caltrans.

The abandoned stretch of Highway 1 will eventually become a hiking, biking, and pedestrian trail maintained by San Mateo County.

To celebrate the opening of the tunnels, Half Moon Bay Brewing Company also held community celebration Monday to unveil its new beer, “Tunnel Vision Ale.”

MORE NEWS: Man Seriously Injured In South Berkeley Hit & Run; Driver Sought

(Copyright 2013 by CBS San Francisco and Bay City News Service. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)