Community Government Transportation

Q&A provides details on cost, possible roundabout and more in Fox Island Bridge replacement

As Gig Harbor Now reported last week, Pierce County has released final Type, Size, and Location Study looking at options for replacing the Fox Island Bridge. After that story’s publication, the county provided expanded answers to questions we submitted earlier on the topic.

The following Q&A shares that additional information, which touches on (among other things) bridge replacement cost and a possible roundabout at the intersection of Warren Drive NW and Fox Island Bridge Road NW.

“The existing Fox Island Bridge is at the end of its serviceable life and must be replaced,” the study concludes.

Construction could start in 2030 or 2031, but this enormously expensive task is not a certainty in the near term. Pierce County reserves the option of continuing to maintain and repair the existing bridge, and deferring replacement for up to 20 years.

And when bridge replacement does move forward, the roundabout under consideration at Warren Drive and Fox Island Bridge Road should not be viewed as the county’s final design choice for the intersection, a Pierce County Planning & Public Works spokesperson emphasized. Instead, it is “an option that can be removed as the project progresses.”

The answers in the following Q&A come from Ben Norton, Pierce County’s bridge engineering supervisor.

Q: In the final Type, Size, and Location study, Table 5-4 provides updated costs for the three bridge alternatives: a new 2,000-foot bridge on the east side of the existing span; new 2,000-foot bridge close-in on the west side; and a new 3,000-foot span on the west that starts and ends near the existing bridge but bulges westward as it crosses Hale Passage.

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

In the report, right-of-way costs for the 2,000-foot east alternative, at $16.7 million, are markedly higher than right-of-way costs for the 2,000-foot west alternative, which are $9.6 million. What’s the reason for the 2,000-foot east alternative’s higher right-of-way costs? Is it because there are more homes, including more valuable homes, close to the existing bridge’s eastern side?

A: While the total number of properties impacted by each alternative is very similar, the specific properties impacted by each alternative are different. In the case of the “east alternative,” a preliminary analysis using publicly available data showed that properties impacted east of the existing bridge appear to be more valuable, on average, than the properties west of the existing bridge. The differences in the estimated right of way costs reflect this observation.

Q: Regarding the roundabout that is recommended at the intersection of Warren Drive and Fox Island Bridge Road — the Final TSL study says that there have been five crashes (w/ property damage only) over the last 10 years involving cars running off the road at the intersection of Warren Dr. and Fox Island Bridge Road.  Is that a particularly high number of crashes, and is this frequency of crashes the primary reason a roundabout is being recommended?

The five crashes you reference can be attributed to the sharp horizontal curve on the existing roadway that transitions Warren Drive to the east with Fox Island Bridge Road, which just happens to be near the intersection. These crashes were caused by drivers failing to safely navigate that curve and running off the road, likely due to excessive speed or distracted driving. This indicates that the existing roadway geometry at the Fox Island Bridge Road and Warren Drive NW intersection could be contributing to this accident history.

The sharp curve on Warren Drive leading to the Fox Island Bridge. Photo from the Type, Size and Location study.

Five crashes in ten years is not unusually high. However, given the concentration of these accidents in the same location, the similarity in crash type, and the fact that this is generally considered a low-volume roadway, it is noteworthy and an element that any proposed design should try to improve.

This crash history did not directly contribute to the roundabout layout, but the roundabout design would eliminate the underlying geometric condition contributing to the crash history. It’s well-documented that roundabouts are a much safer intersection design than either signalized or stop-sign controlled intersection, so the roundabout design would be safest design option available at this site. 

Q: Can you speak to any other reasons the roundabout is being recommended?

A: There are several design considerations noted in the answer to the question below that indicate the roundabout offers advantages over other alternatives. Beyond that, it is important to note that at this preliminary level of design, it is best to advance the designs that require the largest physical footprint as we move into the environmental permitting phase. Design refinements can easily decrease the footprint without impacting the environmental permitting. However, increasing the footprint during or after the environmental process will delay the environmental permitting process.

Q: For example, does the fact that this major bridge construction will be underway in this location make it an especially convenient time to create a roundabout there (i.e. equipment will be in place, there will already be some traffic disruption, etc.)?

A: Replacing the Fox Island Bridge necessitates the reconstruction of the Fox Island Bridge Road/Warren Drive intersection, regardless of which alternative is chosen. The existing intersection configuration cannot be replaced in-kind because it would not conform with current design criteria.

To comply with current requirements, only two options are viable: a roundabout or a T-style intersection (either signalized or stop-sign controlled) in which Fox Island [Bridge] Road meets a continuous east-west Warren Drive. As noted above, the roundabout option would be safer, but it does require a larger physical footprint.

The most significant difference between the two options is that the westbound Warren Drive to southbound Fox Island Bridge Road movement would have to turn left at either a stop sign or a signal, whereas today this is a free flow movement. By contrast, the roundabout design perpetuates a near free flow condition. Because this is one of the largest volume movements at this intersection during the evening commute, the roundabout responds best to the traffic patterns in the area with minimal-to-no queuing of vehicles and is the safer of the two options.

In addition to these operational considerations, there are also advantages to building the roundabout during construction to keep traffic flowing over the existing bridge while the new one is being built. The roundabout has built in “detours” within the circular intersection roadway, whereas a T-intersection may still require temporary pavement bypasses and additional right of way to keep traffic flowing during construction. 

Q: Can you provide a cost estimate for the roundabout?

A: At this preliminary stage, our estimated cost for construction of the roundabout is about $2 million. There are many variables and unknowns that could impact the final cost as the project moves forward.

Q: Will including the roundabout in the project increase the net physical footprint of the project (i.e. will more right-of-way have to be acquired, compared to not having the roundabout as part of the project)?

Refer to responses to question 2 above. The roundabout does require a larger right-of-way for the intersection compared to a T-intersection, but temporary detours required to construct the T-intersection may increase the footprint, making the difference between the two options relatively small.

At this stage, we do not believe the roundabout would increase the number of total property acquisitions compared to the T-intersection alternative. The total acreage of new right-of-way may decrease, but the difference would only occur on properties where sliver parcels are required.

We appreciate and understand the community’s questions about the intersection options. As part of the environmental permitting phase of the project, which is expected to start next month, the County will be fully developing the T-intersection alternatives and comparing those with the roundabout designs. This information will be shared at an upcoming public meeting, which we hope to host this summer.

Q: In the roll plots [graphics] used to inform the public at last year’s informational open houses, there were drainage/water quality basins. In the images, they are [shown as] blue elements next to the roundabout on the mainland side, and just south of Bella Bella Drive, on the island. Are these elements what are called “swales” and are discussed in the Final TSL Study Appendices (Appendix I, 2024 Bridge Deck Drain and Water Quality Memo; click here and scroll to page 334 to view)?

A: Basins and swales are technically different but can be used independently or together as part of a water treatment system. As you noted in the comment below, a swale is best described as an engineered channel system that transfers and treats stormwater, whereas a basin is a hole where water is collected and is treated through settling and percolation into the ground. Either or both can be used in a comprehensive water treatment design depending on the pollutants being targeted.

The Appendix I memo was developed before the alternatives were designed to get rough estimates of how much acreage would be needed to treat our stormwater volume. The alternatives were then laid out using this information. While the roll plots only show the basins, it is reasonable to assume that some swales may be used to drain the water from the road to the basins for treatment. Those are not shown for clarity in the roll plot graphics.

Q: Some neighbors of the bridge who are concerned about being displaced wondered about the size of the planned swales (in the context of concern over the total footprint for the project). There are some tables in the Appendices volume of the Final TSL that appear to speak to this size question. Specifically, Appendix I, Table 4 (click here, page 340), appears to indicate that the swale on the mainland side will be 90 feet long at its bottom and 13 feet wide, including side slopes; the swale near Bella Bella Drive on Fox Island would be 110 feet long at its bottom and 19 feet long, including side slopes. Is this an accurate interpretation of the table?

A: Yes, this is accurate with one important caveat: at this preliminary stage of design, these are only approximate values. A detailed drainage and water treatment analysis will be necessary during the final design of this project to refine these dimensions.

Like the roundabout approach, the water treatment facility sizes illustrated depict the largest possible footprint for the environmental permitting. The final design work could reduce these to the smallest size necessary to treat the storm water and to minimize right-of-way requirements.