Tunnel work starting

A bypass for the stretch of highway was first envisioned back in the late 1950s or early 1960s, Weiss said. However, in the 1980s after a number of long-term road closures, "the importance of somehow building around

existing Highway 1 was evident," Weiss said.

Caltrans originally proposed an overhead bypass, but the idea had "a number of problems," including environmentalists' concerns about its proposed route through a state park and over an undeveloped mountain.

The tunnel plan for rerouting the stretch of highway took hold after a severe slide in January 1995 closed the road for approximately five months, forcing commuters through lengthy detours and cutting off revenue to businesses along the stretch. Caltrans spent $1.5 million repairing and stabilizing the roadway, inserting long rock bolts below the ground to stabilize the rocks and bolting a steel net to the road to catch rocks loosened by rains. And while the road has lasted through several rainy winters, Caltrans warns that the repairs are only temporary.

"The larger issue is the subsidence that occurs below the road," Weiss said. "The road as it exists yesterday is 40 feet below the level of the road 30 years ago. That just underscores why we need to bypass the existing Highway 1."

In 1996, San Mateo County voters passed Measure T, deeming the tunnel the chosen alternative to bypassing Devil's Slide.

The project is funded primarily by federal emergency funds, with less than 1 percent of the money coming from the State Transportation Improvement Program. The first $150 million installment in federal funding arrived this spring and a similar installment is expected next year.

The project is expected to take about six years to complete, according to Weiss. When the tunnel project is through, Caltrans is expected to deed the original section of Devil's Slide highway to the county of San Mateo for use as a hiking and bicycle path.

The invitation-only groundbreaking ceremony will take place at 2 p.m. Friday at Grey Whale Cove.