Two Fremont BART Bridges, Two Very Different Engineering Problems
By Matthew Martinez, Founder, CEO & Managing Broker, Diamond Real Estate Group. California DRE #01869679.
Two bridges associated with BART’s expansion through Fremont solve very different problems. The Walnut Avenue rail bridge had to address fault movement, while the Warm Springs west-access bridge had to carry people across active railway tracks beneath high-voltage lines.
Both belong to the local transportation network, but their form follows different constraints. Comparing them offers a clearer view of infrastructure than treating every bridge as simply a span between two points.
The Walnut Avenue bridge responds to a fault-zone setting
HNTB’s first-party design account identifies the Walnut Avenue Bridge as part of the 5.4-mile Warm Springs extension from Fremont Station. The designer describes its position across the Hayward Fault and the need to accommodate substantial differential ground movement.
The project used a post-tensioned concrete through-girder bridge with short abutments supported on mechanically stabilized earth walls. HNTB also identifies a load-transfer slab beneath the wall supporting the southern abutment.
These are connected components rather than independent construction details. The bridge, its supports and the ground-support system had to be considered together because the engineering problem involved movement beneath the structure.
The design objective differs from an ordinary static crossing
The designer’s account emphasizes analysis of seismic scenarios and collaboration with BART, the contractor and UC Berkeley. The published aim was to retain a recoverable rail connection after severe fault displacement.
That is a specific infrastructure design objective. It does not establish the performance of a nearby house or guarantee a particular recovery time for the whole railway. A bridge is evaluated through its own configuration and design criteria.
The west-access bridge solves a different barrier
The City of Fremont’s 2022 project account describes the Warm Springs/South Fremont pedestrian bridge crossing five sets of Union Pacific tracks. Its purpose is to connect the station with the developing Innovation District to the west.
The bridge uses both a truss span and a cable-stayed section, linking to a plaza through stairs, escalators and an elevator tower. It is therefore a sequence of horizontal and vertical connections, not just the bridge deck itself.
For someone arriving from the west, the new connection changes the usable geography around the station. A station can be physically close while a railway corridor prevents a direct approach.
Overhead lines influenced the bridge’s form
The engineering association’s 2023 awards announcement describes the design by Biggs Cardosa Associates. It explains that the combined truss and cable-stayed arrangement addressed a constrained site with high-voltage lines overhead.
The announcement also describes staged fabrication and lifting while maintaining clearances around the existing tracks and station. The construction process was part of solving the site, rather than something considered only after the form had been selected.
The bridge name does not explain the whole journey
The two projects operate at different scales. One carries trains through a difficult ground condition along the extension. The other helps people reach a particular station across a local barrier.
For a homebuyer, that distinction is useful: regional transport availability and the practical approach from a specific property are related but separate parts of a daily trip.
Explore real estate and home for sale in Fremont and our community and housing comparison. Contact Diamond to compare homes through their actual street connections and transportation setting.
Sources checked October 28, 2026. Engineering descriptions are attributed to project participants and do not constitute a property-specific seismic assessment.
