Northern Segment

The Transportation Authority of Marin, in cooperation with Caltrans and the City of Larkspur, completed the new 915-foot pedestrian and bicycle bridge that spans Corte Madera Creek. The bridge replaces a narrow and substandard sidewalk with a 12-foot-wide multi-use path that connects with Sir Francis Drake Boulevard and the Larkspur ferry terminal to the north. The structure features thoughtfully designed viewing alcoves that invite users to pause and take in views of San Francisco Bay and the surrounding environmentally sensitive salt marsh habitat.

Innovative design was essential to achieve two primary objectives in this project: first, to provide a Class 1 multi-use path without placing new or temporary support columns in the environmentally sensitive creek, and second, to provide a path that does not exceed a maximum grade of five percent. SGA was the bridge architect and designed the pathway geometrics and architectural elements.

The use of preexisting outrigger caps, from a prior retrofit, provided the width necessary for the path, and custom precast girders were employed to bridge the gap. These precast girders served a dual purpose, offering an over-water platform during construction, while eliminating the need for additional supports within the creek. Supporting corbels were placed on the outrigger caps, allowing the precast girders to be placed at customized elevations to achieve traveled way slopes appropriate for a bike/ped facility.

The most formidable challenge was the need to maintain 21 feet of vertical clearance beneath the bridge for the navigation channel below. To overcome this challenge, the design team developed a pair of vertically haunched and horizontally curved “L-shaped” precast reinforced concrete girders. The resulting precast span is one-of-a-kind and an architectural highlight that serves as a bridge focal point and gives the center span a distinctive appearance.

The North-South Greenway Gap Closure project was awarded the Active Transportation Project of the Year by the California Transportation Foundation and Outstanding Bridge Project by the American Society of Civil Engineers, San Francisco section.

Southern Segment

Sponsored by the Transportation Authority of Marin (TAM), the County of Marin’s North-South Greenway Gap Closure Southern Segment project would connect the Northern Segment project to the bike/ped paths at the intersection of Wornum Drive and Redwood Highway, at the border between the City of Larkspur and the Town of Corte Madera. SGA studied two routes for the connection’s multi-use path: one that remained on Redwood Highway and the other that followed a disused railroad adjacent to the wetlands. SGA developed and assessed over 15 alignment alternatives and recommended the route that would follow the railroad right of way, owned by the Sonoma-Marin Area Rail Transit (SMART) district. Linking to the Northern Segment project near Corte Madera Creek, the proposed path would connect to SMART’s elevated railroad berm via a future public easement through private property and a new bridge. A variety of constraints and considerations influenced the project design, including minimizing disruptions to adjacent private residences, preventing access into sensitive marshland habitat, and grading the pathway for proper stormwater drainage. While the use of the SMART right-of-way has been secured, acquisition of a public access easement through private property is still required. Preliminary engineering and environmental review for the project was been suspended while the project sponsor resolves funding constraints of the overall North-South Greenway Gap Closure Project.