A long-planned tunnel to bypass the landslide-prone Last Chance Grade on Highway 101 is moving into the design phase after California approved $180 million for the project.
The tunnel would run east of the existing highway in Del Norte County, providing a more reliable route when landslides threaten or close the corridor.
At about 6,000 feet, it would be the longest tunnel Caltrans has built, about 1,800 feet longer than each of the Tom Lantos Tunnels in the Bay Area.
Del Norte County Supervisor Chris Howard said closures at Last Chance Grade force travelers to take an eight-hour detour.
“It’s just not acceptable — just not acceptable at all,” Howard said.
Last Chance Grade has been plagued by landslides for decades. The instability has repeatedly damaged Highway 101 and forced lengthy traffic restrictions. The highway returned to two-way traffic in 2023 after about nine years of one-way traffic control.
Howard said the California Transportation Commission asked difficult questions about the size of the allocation, which he said was unusually large for a design and engineering project.
He and other North Coast officials argued that the funding is critical to finding a permanent solution for the highway.
“This coalition has worked on this project for the last decade to come up with a tunnel as a way to essentially avoid impacts to some of the world's most protected resources, which are old-growth redwoods,” Howard said.
Much of the affected highway runs through Redwood National and State Parks.
The project has now entered its design and permitting phase. Some of the work will involve geotechnical investigations to better understand the ground surrounding the proposed tunnel.
Howard said engineers need to determine the location of underground slip planes so the tunnel can avoid unstable areas.
The commission also allocated $1.5 million for right-of-way work.
Construction is scheduled to begin in 2031.
