What is Alternative F?
Alternative F features a tunnel that avoids the landslide hazard and limits impacts to natural and cultural resources at the north and south portals. The proposed tunnel would be approximately 1 mile in length with one lane in each direction along with bike/pedestrian facilities. Some of the features would be similar to the Tom Lantos Tunnels at Devil’s Slide on Highway 1, south of Pacifica in San Mateo County, California.
Why Was Alternative F Selected for Further Study?
The tunnel would provide more stability and reliability by avoiding the landslides. The tunnel would pass deep under an area of significant natural and cultural resources, greatly reducing potential environmental impacts. Use of sequential excavation methods would reduce the construction impacts and the amount of soil to be hauled off-site. While the tunnel alternative is significantly higher in cost than Alternative X, it was not higher than the cost of other alternatives analyzed. It also would have the smallest environmental footprint of all alternatives studied to date, which would limit potential environmental resource impacts.
Key Project Features
Anticipated time to constuct: 6-8 years
Estimated cost to construct (year 2031$): $2.1 billion
Associated Impacts to Key Resources
Permanent impacts to:
Redwood Forest: 0.64 acres
Sitka Spruce Forest: 0.20 acres
Red Alder Forest: 2.97 acres
Anticipated Large Trees Removed:
Red Alder: 40
Douglas Fir: 9
Sitka Spruce: 49
Coast Redwood: 39
Western Hemlock: 7
Total: 144
Permanent Impacts on Wetlands/Waters:
0.38 acres
On the map, the alternative is denoted with a letter.
The red line indicates the current LCG alignment and the dark pink segment with yellow border indicates the approximate position of the tunnel.
Please note the following:
- The lines on the map are approximate and do not indicate the exact placement of the alternative.
- Costs are estimated and include construction, materials disposal, and mitigation.