What is Alternative F?
Alternative F features a twin-bore tunnel with cross-passages that avoids the landslide hazard and limits impacts to natural and cultural resources at the north and south portals. The proposed tunnel would be similar in length and features 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 tunnels would provide more stability and reliability by avoiding the landslides. The tunnels would pass deep under an area of significant natural and cultural resources, greatly reducing potential environmental impacts. Use of tunnel boring machines 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.
Construction length: 2.3 miles
Construction footprint: 5 acres
Construction schedule: 7 years
Estimated construction cost: $1.3 Billion (2021 costs)
Length within parks: 0.5 miles (portal approaches at north and south portals)
Existing Habitat Type in Construction Area
Coastal scrub/grassland /spruce: 2 acres
Riparian: 0 acres
Clear cut: 0 acres
Young Redwood Forest: 0 acres
Mature Redwood Forest: 1 acre
Old Growth Redwood Forest: 1 acre
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.
- The acreages of “Existing Habitat Type” are estimates based on overall analyses of habitat types in the area.
- Costs are estimated and include construction, materials disposal, and mitigation.