A resilient coastal connection that puts people first
At a glance
GHD supported the County of Humboldt, as the designer, engineer and environmental lead on the Humboldt Bay Trail South project. The goal was to create a safe, fully separated, Americans with Disabilities Act (ADA)‑accessible connection between Eureka and Arcata through one of California’s most constrained coastal corridors. The 4.25‑mile Class I multi‑use trail supports everyday travel and recreation while protecting the environmental sensitivity of Humboldt Bay and strengthening resilience to flooding and sea-level rise.
The project also advances a important segment of the planned Great Redwood Trail, contributing to a broader statewide vision for a continuous public trail system while preserving future rail use within the corridor.
The challenge
Delivering a continuous Class I multi‑use trail between Eureka and Arcata presented a combination of physical, environmental and operational limitations. The alignment is tightly constrained by US Highway 101 on one side and coastal wetlands and Humboldt Bay on the other, leaving little room for error. Large sections of shoreline had a history of flooding, erosion and structural degradation, placing both existing infrastructure and future trail users at risk.
A critical obstacle was maintaining uninterrupted trail continuity across Eureka Slough without forcing users into high‑risk highway crossings. Replacing the existing railroad bridge was not viable due to cost, environmental impact and the need to preserve rail operations.
Subsurface conditions added further complexity. Soft bay margin soils required careful geotechnical solutions to manage settlement and long‑term performance, particularly for new bridge structures and raised corridor sections. All elements needed to meet modern safety and ADA-accessibility standards along the full 4.25‑mile corridor, while navigating complex permitting and construction sequencing within environmentally sensitive areas.
The corridor’s sustained exposure to storm-driven overtopping and coastal flooding posed a significant risk to any improvements. Past events had already impacted both the rail line and adjacent US Highway 101, underscoring the need for a solution that performs under rising coastal hazard pressures.
Our response
Our project team approached the trail as a regional transportation facility rather than a recreational amenity, integrating transportation, structural, geotechnical, coastal and environmental disciplines into a single, cohesive delivery approach.
To maintain continuity across Eureka Slough, the 725-foot active railroad bridge was converted to support shared rail and trail use. This avoided full replacement, maintained limited rail operations and created a safe, uninterrupted crossing for trail users. A rubber flangeway filler system delivers a smooth, ADA-accessible surface while remaining compatible with rail use.
Our design addressed flood risk and strengthened long-term resilience by repairing around 6,600 feet of shoreline revetment and raising sections of the railroad prism through the most exposed reach. Working within existing footprints helped restore protective function while limiting environmental disturbance.
Further improvements at Brainard Slough restored hydraulic performance. Failed culverts and debris were removed to improve fish passage and reduce erosion risks affecting the trail, rail corridor and nearby highway.
Throughout the corridor, the team applied context-sensitive design, carefully managing grades and cross slopes and allowing enough width to support mixed user speeds and high use. The result is a fully separated, ADA-accessible facility designed for durability, safety and reliable performance in a demanding coastal environment.
The impact
Opened to the community in June 2025, the project delivers a continuous, 4.25-mile Class I multi-use trail that replaces a previously unsafe highway shoulder route with a safe, low-conflict corridor for people walking, cycling and using mobility aids.
The completed trail connects the Eureka Waterfront Trail and Humboldt Bay Trail North, creating over 14 miles of continuous nonmotorized facility.
Beyond mobility, the project strengthens coastal resilience by stabilizing vulnerable shoreline segments and improving flood resistance along a critical transportation corridor, supporting both trail users and adjacent infrastructure as sea levels rise and extreme weather events increase.
As a completed link in regional and statewide trail networks, the corridor expands access to the Humboldt Bay shoreline for more connected communities. It demonstrates how thoughtfully engineered active transport infrastructure can function as essential public infrastructure, delivering safety, accessibility and long‑term resilience even in highly constrained environments.
The project also highlights how existing transportation infrastructure can be adaptively reused to deliver high-performing, multimodal solutions while preserving long-term corridor flexibility.
As agencies rethink how people move, we’re working with teams facing similar challenges. Learn more about our work in transportation infrastructure.