Highways and major roads have an unfortunate habit of cutting through public open space to create disruption and separation. But occasionally that separation is reversed and connectivity re-established. Such an example is the Presidio in San Francisco. When the Golden Gate Bridge opened in 1937, the highway forming the southern approach cut through the Presidio, separating the army base on the higher ground from Crissy Field airstrip located along the foreshore of San Francisco Bay.
As long as the Presidio remained a military base, the separation was not a big problem. However, when base was decommissioned in 1994 and the Presidio Trust was created to manage the whole site as public open space, the lack of connectivity between the former army base and the foreshore became a major issue.
As it happened the highway needed replacement due to a number of design flaws and damage from the 1989 Loma Prieta earthquake. This provided an opportunity to reconfigure how the highway sat in the landscape. Various road-centric plans were initially considered, but a proposal from a Bay Area landscape architect named Michael Painter was adopted. The concept provided for the highway to be realigned closer in to the slope along the edge of the former military base and to enclose a section of it in tunnels with parkland extending over top and linking the two sections of the Presidio.
The concrete tunnels containing a section of the highway were completed in 2015 when I visited the Presidio in June of that year and met with Michael Boland, Chief of Park Development and Operations. It was expected that landscape works would proceed immediately to implement the winning design prepared by James Corner Field Operations and covering some 5 hectares. However, implementation was delayed when the cost estimate significantly exceeded the available budget. Fortunately the additional funding was obtained and implementation of Corner’s design is now proceeding. Photos that I took during a visit in April 2018 show machinery at work placing soil over the tunnels and drainage being installed.
The design features a terraced landscape that climbs up from marshlands of Crissy Field along the foreshore to gently crowned tunnel tops, where a series of lawns, meadows, and sweeping pathways are interspersed with small gardens and nooks that block the breezes off the water. The new ground over the tunnels will be about 10 metres higher than most of foreshore, providing spectacular panoramic views.
A rendering of the design concept on exhibition in the Presidio Visitor Centre provides an indication of the scale and context of the Tunnel Tops project with more information including videos on the project web site https://www.presidio.gov/tunnel-tops.
The landscape plantings aim to recreate the vegetation communities that existed on the site before the highway cut through it. More than 50 native plant species collected throughout the Presidio are now being cultivated in the on-site nursery for use in the landscaping works. Various grasses and succulents will blanket the tunnels, and the bluff leading down toward the water will be covered in native shrubs and grasses like those seen on top of other escarpments along the edge of San Francisco Bay. It is intended that these plant communities will create habitat for the diverse range of bird, butterfly, and insect species at the Presidio. What was once a divisive highway will become public open space connection with a distinctive natural landscape character.
