MH-FB TIMP - Alexander Avenue and Danes Drive Intersection Improvements, Marin Headlands
UPDATE 7/11/12: The Finding of No Significant Impact (FONSI) is now available. Click the Document List link to the left, then click on the document title. In addition to the FONSI a Response to Public Comments is also available in the same location.
The National Park Service (NPS) and Golden Gate Bridge Highway and Transportation District (GGBHTD) partnered to plan and conduct the environmental analysis for the proposed project. A joint Environmental Assessment/Initial Study (EA/IS) was prepared in accordance with NEPA and the California Environmental Quality Act (CEQA). This FONSI approves federal actions on NPS property only. GGBHTD issued a separate Notice of Determination for project actions on state land.
The purpose of the project is to correct existing deficiencies and substandard roadway conditions at the Alexander Avenue left-turn lane to Danes Drive. The project identifies actions within the project area that address a number of deficient multi-modal transportation conditions including: inadequate roadside shoulder width to handle shared bicycle, pedestrian, and automobile use; and skewed intersection geometry.
NPS and GGBHTD have selected Alternative D, the 8-Foot Rockfall Catchment Alternative, for implementation.
Alternative D will allow for two 12-foot-wide vehicle lanes, a 12-foot-wide left turn lane, and a 5-foot-wide combined shoulder and bicycle lane on both sides of Alexander Avenue. Alternative D will install a temporary rockfall barrier between the catchment ditch and roadway. Any change to the temporary barrier (removal of the temporary barrier, possible installation of rockfall mesh, or installation of a permanent barrier) will be subject to a separate environmental evaluation (undertaken by NPS and the Federal Highway Administration Central Federal Lands Highway Division) prior to implementation. This alternative will result in a final east cut slope height of approximately 77 feet and the total width of excavation will be approximately 91 feet. Figure 2-3 of the EA/IS provides a cross-sectional view looking north along Alexander Avenue of the proposed rock cut for Alternative D, including slope angles, finished slope height, and width of excavation.
Excavation of the rock cut will occur during the first phase of construction to provide additional space to ensure that one traffic lane in each direction could remain open during subsequent phases of construction. During this initial construction phase traffic wil be routed to the furthest west section of the roadway.