Community Government Transportation

Fox Island Bridge replacement details emerge in Pierce County’s newly-released study

Like the view of Mt. Rainier when the fog lifts over Hale Passage, details of the proposed new Fox Island Bridge grew clearer last week when Pierce County released its long-promised final Type, Size, and Location Study for the bridge replacement project.

The final TSL study, prepared by consultants HDR Engineering, adds precision to discussions of a new Fox Island Bridge’s expected size and price tag.

It stops short of endorsing any of the three proposed locations under consideration for the new span. It also reiterates the Pierce County’s position that a new bridge, in the near term, is no certainty. The county may still pursue a deferral option in which it keeps patching up the old, deteriorating bridge for as long as 20 years before replacing it.

But if the project moves forward with one of the three “build” options that are now on the table, with construction beginning in 2030 or 2031, the report tells which would be the least expensive route.

The Fox Island Bridge as seen from the east, facing the mainland. Photo by Ted Kenney

Roundabouts and swales

And it fleshes out other aspects of the three bridge replacement scenarios that were addressed only tangentially before. For example, at public open houses last year, the county presented graphics showing new project features including a traffic roundabout on the mainland and stormwater basins at both ends of the proposed new span.

While county officials previously emphasized that the roundabout was just a “possibility” at the intersection of Warren Drive and Fox Island Bridge Road, they’re now calling it a “key design feature” and recommending that it be included in a new bridge design.

As for the stormwater basins, the report gives them a technical name — “bioretention swales” — and notes that they will measure up to 110 feet long and 19 feet wide.

The size of these features matters to project stakeholders, especially neighbors of the proposed new bridge. They worry the roundabout and stormwater basins could contribute to a larger project footprint. That would require the county to acquire more right-of-way and affect – or even displace – more homeowners.

Pierce County has said consistently, and repeats in this study, that the project will “impact” between five and 10 properties. Potential effects range from temporary use of land during construction to blocking views. In some cases, the project might require demolishing houses and relocating their occupants. In all instances, the county must compensate affected property owners at fair market value.

Options

Since last spring, the county has referred to three possible bridge replacement options: a 2,000-foot span hugging the west side of today’s crossing; a 2,000-foot bridge built near the old structure’s east side; and a 3,000-footer that starts on the mainland just west of today’s crossing and bulges further to the west as it crosses Hale Passage.

The Final TSL Study replaces the 2,000- and 3,000-foot estimates with actual end-to-end lengths. These measurements are 2,336 feet long for the close-in, west side span; 2,254 feet for the replacement bridge east of today’s crossing; and 2,976 feet for the longer bridge that arcs westward.

This image from the final Type, Size and Location study shows three potential routes for a new Fox Island Bridge. The report clarifies that the actual lengths are 2,976 feet (green option), 2,336 feet (yellow option), and 2,254 feet (red option). Source: Pierce County.

The shortest bridge would not be the least expensive. According to the report, building the 2,336-foot span on the west side would cost $302.1 million. That would save $3.8 million in design, construction and right of way costs compared to building the shorter 2,254-foot option just east of today’s bridge. (Estimates for design, construction and right-of-way costs are in 2031 year of expenditure dollars).

Among other possible savings, the report projects right-of-way costs to be 43 percent lower ($9.6 million vs. $16.7 million) if the county chooses the short option on the west side of today’s bridge over the shorter route on the east side.

The longer 2,976-foot bridge, bulging westward into Hale Passage, was the most expensive “build now” option, at $373.7 million for design, construction and right-of-way.

Cost calculations for the three bridge alternatives. source: Pierce County.

Superstructure and substructure

Pursuing any of these replacement options would likely involve the use of tons of pre-made concrete components, the TSL study makes clear.

In the report, the county recommends building the bridge’s superstructure – that is, the upper part of the span that directly carries traffic loads – from concrete structural members. Specifically, the report envisions using either pre-cast prestressed concrete or pre-cast post-tensioned spliced concrete girders.

Advantages of using both these types of components include “cost, local contractor familiarity, maintenance, service life, the reduced number of in-water piers (which impact cost and schedule, and environmental impacts), and future deck replacement,” the report states. The choice between these materials “will depend on future geotechnical data, more advanced design, and market conditions at the time of bidding.”

The Manette Bridge in Bremerton is an example of precast post-tensioned (PC/PT) concrete girders, which are a leading candidate for use in a new Fox Island Bridge. Source: Pierce County.”

However, Pierce County reserves the right to go in a different direction if needed. It could use a lighter steel composite superstructure to “allow reduced foundation sizes” if the county encounters poor geotechnical conditions, the report says.

For the bridge’s substructure — the foundation and support structure beneath the bridge deck — the county is only considering using concrete columns supported by deep foundations. These “perform well in high seismic zones, are durable, and are familiar to local contractors,” the report says.

‘Key design feature’

Pierce County’s idea of installing a roundabout at the intersection of Warren Drive and Fox Island Bridge Road made its public debut in graphics shown at the open houses last year. The county’s position then was that this feature was under consideration as part of the bridge replacement.

But the final TSL study goes a step further, calling a one-lane roundabout a “key design feature” that is recommended in all three build scenarios.  The roundabout “would naturally slow vehicle speeds, improve sight distance, reduce crash severity, and improve pedestrian safety with minimal traffic delays,” the report says.

In the replacement scenario featuring a new bridge situated east of the existing one, this roundabout would shift further north compared to the other two options.

The report does not specify whether adding a roundabout increases the project footprint. But in an interview, county Bridge Engineering Supervisor Ben Norton confirmed that a roundabout or new stoplight-controlled intersection (another option at this location) would require more space than the current intersection, which has a stop sign.

Just how hazardous is the intersection? From 2014 to 2023, “there were five crashes involving single cars running off the road at this location, indicating that sight distance and the geometry of that curve may be a contributing factor,” the report states. The accidents resulted in property damage only.

This risk does not appear to be increasing. “2024 traffic volumes in the study area are very low and have not grown over the last six years. This trend is expected to continue as the area is largely built out under the existing zoning,” the report says.

Stormwater

Stormwater runoff from the existing Fox Island Bridge drains directly into Puget Sound. That was a common disposal solution when the bridge was built in 1954. But today’s design practices require treatment of runoff before discharging into the bay. As a result, runoff will be collected from any new bridge between Warren Drive on the mainland and Bella Bella Drive on the island, and carried to a treatment location.

Graphics produced by the county last year showed the stormwater treatment features as blue ponds. They are west of the proposed bridge approaches, adjacent to Bella Bella Drive on the island and to Warren Drive on the mainland.

The final TSL study clarifies that these are bioretention swales, which are shallow, landscaped channels designed to filter and soak runoff into the ground. Such swales are linear but can curve or follow site contours rather than running in a straight line.

The report notes that the larger of these swales, on the Fox Island side of the proposed new bridges, would measure some 110 feet along its bottom, with a width of 19 feet, including side slopes. Bridge engineer Norton noted that the county may need to add some additional land to each of the swales to facilitate entry by county staff, who will need to mow the grass inside.