The North-South Greenway Gap Closure project, in Marin County, California, is emblematic of a regional commitment to fostering alternative modes of travel, while championing a healthier, more sustainable transportation system.
The Transportation Authority of Marin, in cooperation with the California Department of Transportation 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. Southward, the path continues to link up with existing and planned multi-use paths in the area and will be designated as part of the Bay Trail network. Additionally, 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.
The enhanced facility not only fosters accessibility but encourages users to take advantage of Marin County’s major public transportation hubs, such as the Larkspur Ferry Terminal, Larkspur SMART station, and local and regional bus stops along the US 101.
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.
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 to comply with the Americans with Disabilities Act, allowing the precast girders to be placed at customized elevations.
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.
Moffatt & Nichol served as the prime consultant and engineer of record for this regional multimodal project, which serves as a model for prioritizing active transportation initiatives within a community.
As evidence of this, 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. These awards of recognition mark a significant milestone in the ongoing efforts to build a more extensive nonmotorized transportation network.
An overview video of the project can be found here.
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