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| Project Description |
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The Tunnel is to be two lanes with shoulders and median, conforming to State Coastal Act and Local Coastal Program requirements for Highway 1 as a two-lane scenic highway. It will be approximately 4600 ft. (less than a mile) long with a grade of 1.5-2%. The Tunnel would run from the top of Shamrock Ranch in Pacifica , behind Devil's Slide and through San Pedro Mountain to about 1000 ft. north of Green Valley and the Montara State Beach/McNee Ranch Park Boundary where it would rejoin Highway 1. The existing roadway on either side of the tunnel portal approaches will remain unaffected. |
The bypass would be 4.5 miles long with grades of 6.5%, roadbeds 76-106 ft. wide, and paved for two lanes with shoulders, uphill passing lanes, downhill vehicle escape lanes, and overlook access lanes. Starting at the Linda Mar Intersection in Pacifica, it would travel through Shamrock ranch, across the southern face of San Pedro Mountain, enter McNee Ranch State Park at the "saddle pass", swing westward to the overlook ridge, then back east to cross Martini creek, then finally back west where to rejoin the existing highway about 1000 yards north of the Chart House Restaurant in Montara. |
| Excavation |
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160-200,000 cubic yards of earth will need to be excavated for the tunnel, less than 5% of the earthwork required for the proposed bypass. The material will be used to construct the approaches at each end, so little or no material will need to be trucked away or brought in. |
To create the proposed bypass roadbed, 6 million cubic yards of material would need to be excavated from 14 cuts up to 280 ft. deep and move and recompacted in 16 fills up to 350 ft. high. The 280 ft. deep, 627 ft. wide, 2100 ft. long saddle cut alone would require more than 9 times the excavation of the tunnel. |
| Impacts |
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The Tunnel will have little visual impact, with only the portals at each end visible. The current road will remain open at all times during construction. As the project does not cross the mountain or enter the open space lands, it will have no environmental or disruptive impacts upon McNee Ranch State Park, surrounding creeks and wetlands, existing or planned residences and developments, the habitats of Montara Mountain or the marine environment. |
The proposed bypass would have significant visual impact, with scars visible from Marin to Pescadero. Over a mile of the existing road would need to be shut down during construction. It would pass directly through McNee Ranch State Park, creating noise and pollution and disrupting trails in 12 places. It would cross sensitive and slide prone wetlands areas, damming uphill canyon drainage and threatening homes below with catastrophic slope failures. It would run through rare coastal mountain environment and over pristine riparian areas. Sediment from construction, cuts and fills would clog creeks and flow out into a Federal Marine Sanctuary. |
| Design, Construction and Environmental Process |
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A supplementary revision of the Federal Environmental Impact Study (FEIS) will be necessary to designate the tunnel as the preferred alternative, taking about 6-12 months (the 1986 FEIS, which changed the bypass design to the current Martini Creek Alignment, took only 9 months.) With virtually no impact on the environment, it is likely an expedited EIR would be issued and approved. Final design and construction will take 2-3 years. |
Although the basic design of the proposed bypass is completed, a substantial amount of redesign is necessary to bring bridges and other structures up to current federal standards. A reevaluation of the existing 10 year old FEIS is required under federal regulation, as well as extensive permitting processes with the Army Corp. of Engineers and other federal and state agencies to disprove that there any better alternatives. Once redesign, reevaluation, permitting, legal and mitigation processes are finished (2-4 years), actual construction is estimated to take 3-5 years. |
| Safety |
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With an alignment about 1500 ft. inland from the existing road and 600 ft. below the top of the ridge, the tunnel will be well beyond any active area of Devil's Slide. The tunnel eliminates the slide danger and curves of the existing road and the steep grades, excessive curvature, steep cliffs and exceptional fogginess of the proposed bypass. Studies have shown tunnels to more stable in earthquakes than surface roads, away from the excessive shaking, roadbed collapse and danger to elevated structures. |
Over 70% of the bypass route is on compacted fill or on elevated structures, the most dangerous areas during earthquakes and the most susceptible to collapse and accidents in bad weather. The proposed bypass summit is in dense fog 53% of the time during peak traffic hours, the average grade is 6.5%, and the total curvature of the bypass is greater than the current Highway 1. These factors, along with a 50 m.p.h. speed limit and no center divider, do not make a very safe road. |
| Cost and Funding |
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The cost of a single bore, two lane tunnel has been estimated by independent sources and by Caltrans as being $50-70M. Emergency funds are already dedicated to the repair of Highway 1 at Devil's Slide. Federal, State, and Local officials and elected representatives have indicated that if the tunnel is chosen as the preferred alternative they will do what is necessary to secure funding. |
As of this writing, the cost of the proposed bypass is $91.3M, based on information collected from Caltrans. Planned engineering expansion of bridge structures and still unspecified mitigation costs and fines from other agencies (State Parks, NOAA, EPA, etc.) will only drive the price tag higher. Only $70M is known to be funded, and the bulk of that is still under the jurisdiction of the Federal Courts. |
