Project Overview

First opened in 1973, Phibbs Exchange has long served as one of the North Shore’s most important transit connections. Following more than a year of extensive upgrades, the expanded exchange reopened in May 2024 with a more accessible and comfortable passenger environment. Today, 13 bus routes serve more than 5,000 customers each day, supported by modern shelters, improved lighting, expanded seating, bicycle facilities and a multi-use pathway.

Connectivity and sustainability were priorities from the beginning. Original designs incorporated sizable daylighted raingardens to manage runoff on site, but operational and accessibility requirements made it clear that not all the proposed facilities would fit. Rather than abandon the project’s rainwater-management targets, the design team moved much of that ecological function beneath the pavement. A total of 462 Silva Cells were installed to manage stormwater while providing lightly compacted soil for 17 new trees — all without reducing the surface area available for buses and passengers.

A Better Place to Wait

A successful transit exchange must do more than move buses efficiently. It must also provide a safe, accessible and comfortable place for people to wait. The redesigned Phibbs Exchange includes larger passenger platforms, modern shelters with increased seating and weather protection, better lighting, improved pedestrian and bicycle connections and space for high-capacity articulated buses.

Trees add another important layer to that experience. In a landscape dominated by pavement, a healthy canopy can reduce heat exposure and make the space between shelters more comfortable during warm summer conditions. The new trees are still young, but they have been positioned throughout the exchange to become a more meaningful source of shade as they mature.

The completed station already feels clean, open and well organized. Its landscaping is fully integrated into the passenger environment without obstructing circulation or boarding areas — a seemingly simple result made possible by putting much of the required ecological infrastructure underground.

Underground Stormwater Management

Daylighted raingardens were an important part of the original stormwater strategy. As the project developed, however, the design team found that the proposed facilities would occupy space needed for passenger loading, accessibility, and station operations. Commuters could not be expected to step from a bus directly into a bioswale, nor could narrow platforms safely accommodate the volume of people moving through the station.

Silva Cells allowed the project team to preserve its ambitious rainwater-management objectives while maintaining a much larger paved surface. Beneath the platforms, the structural system creates protected soil space capable of receiving and treating runoff while supporting the pavement and activity above.

The project sections provide a more detailed look at how the system functions. Runoff from roofs and bus shelters is first routed through catch basins for sediment control before entering the Silva Cell-supported soil. Water is temporarily held, slowed and treated within the soil profile. A minimum 1% slope directs water toward an outlet or overflow connected to the storm system, with an orifice sized to allow the soil to desaturate within 48 hours.

How Water Moves Beneath Phibbs Exchange

Collect: Runoff from roofs and bus shelters is routed to catch basins for sediment control.

Distribute: Captured runoff enters the Silva Cell soil system beneath the passenger platforms.

Slow and Treat: Water is temporarily held within the soil profile, where it is slowed and treated.

Drainage: A minimum 1% slope and controlled outlet direct water to the storm system, allowing the soil to de-saturate within 48 hours.

Shade as Infrastructure

Stormwater management was the immediate infrastructure challenge, but the same Silva Cell soil also gives the station’s 17 trees the resources to grow much larger over time. Each tree has access to approximately 23 m³ of lightly compacted soil — far more rooting space than would typically be available in an isolated tree pit surrounded by pavement.

That soil volume is particularly valuable in a transit environment. Passengers may spend significant time waiting between buses, often with limited ability to relocate during hot weather. As the trees mature, their canopies can extend the station’s shaded environment beyond the immediate footprint of the shelters, cooling more of the surrounding pavement and creating a more comfortable place to wait.

The trees visible in the 2025 photographs are still establishing, as expected only a short time after installation. Their canopies are not yet mature, but they are healthy, well integrated into the finished station and positioned for meaningful long-term growth. The photos capture both what Phibbs Exchange has already become and the cooler, greener passenger environment it is designed to become.

Functional Ecology Beneath Your Feet

The most important feature of the Phibbs Exchange landscape may be the one passengers never see. Beneath the active platforms, soil is simultaneously receiving stormwater, supporting roots and creating the foundation for future shade. Aboveground, the station retains the broad, accessible paved areas required for a busy transit operation.

Both 2x and 3x Silva Cell configurations were used to respond to varying site conditions. The modular system also allowed drainage, conduit, and irrigation to be field-fitted during construction, while the large openings provided access for placing and compacting soil throughout the system.

“Utility integration is easy with Silva Cells.”

— Eric Hagen, Conwest

Phibbs Exchange demonstrates that operational infrastructure and ecological infrastructure do not have to compete for the same limited space. By layering them, the project created a station that can move people efficiently, manage water responsibly and grow progressively cooler and greener with every passing year.