Yukon on track to replace 70-year-old Nisutlin Bay Bridge by 2026

The Yukon government is heading into a second year of construction on the Nisutlin Bay Bridge, with several more years of work on the horizon.

The bridge, which crosses Teslin Lake, Yukon, is the longest bridge on the Alaska Highway. It's also a major infrastructure project, with the government committing $160 million.

Katie Munroe, the director of the transportation engineering branch for the Department of Highways and Public Works, joined the CBC's Elyn Jones on Yukon Morning for an update on the project Friday.

This interview has been edited for clarity and length.

What was wrong with the old bridge, and why does it need to be replaced?

In the Yukon, most of our bridges have a lifespan of around 75 years. The Nisutlin Bay Bridge is currently 70 years old.

We've been doing ongoing maintenance and repairs over the years, but we've just come to a point in time where it makes sense to do a replacement.

And it's not something you can just fix up here and there?

As bridges get older, their ability to carry weight decreases. We already have some weight restrictions on that bridge — but so that we get to a point where we're not really overly impacting traffic flows, we need to do a replacement.

How long is the span of that bridge?

Well, the new bridge will have a span of 483 metres — I believe that's shorter than the existing bridge. It's, I mean, almost half a kilometre. It's pretty impressive.

Tell us how you go about replacing a bridge like this.

Well, it might surprise some people, but in order to build the new bridge, we have to build a temporary bridge.

In order to work over top of the water, the cranes and the other type of equipment used to build the new bridge have to be able to work over the water. They can't use the existing bridge for a couple of reasons: the existing bridge is an enclosed bridge, so the cranes physically couldn't sit on that bridge even if we wanted to. But also, if we had used the existing bridge, it would have some pretty massive impacts on traffic travelling.

So the temporary bridge is created beside where the new bridge will go. If you're in the community, you can see now that some of those spans have been created and the cranes are starting to walk out over the water surface and putting in the piling work.

So a temporary bridge will be created. It will hold the equipment that builds the permanent bridge. Once the permanent new bridge is created, the temporary bridge will be removed.

Just to be clear — the temporary bridge won't have traffic on it at all?

It will never have public traffic. It's only for the construction purposes.

As you build the new bridge, how do you maintain traffic on the bridge and on the Alaska Highway?

The existing bridge won't have impacts to traffic flow from the construction. There might be the occasional lane closure while the contractor moves equipment over the bridge, but generally speaking, it's business as usual on the current bridge.

We're still doing our regular inspections of that bridge, and repairs if necessary, but to the travelling public, you're not going to notice any difference during the construction.

How will the new bridge be different from the old bridge?

It's quite a bit different, actually. It will have a concrete deck which will be paved, so that's an immediate difference. The current bridge has that metal grate that you can hear as you travel over it.

The new bridge will also have wider shoulders that will allow cyclists to cross over safely. It will also have a separated pedestrian sidewalk and lighting. LED lighting will go across the bridge.

Another new feature is there will be a pathway created under the bridge that will allow pedestrians and snowmobiles to be able to pass under the Alaska Highway. So that's a great feature so that people aren't having to cross a busy highway.

And then the last difference is — I made a reference to the weight bearing capacity of the current bridge. The new bridge won't have any load restrictions because it will be, you know, significantly stronger.

Right now, what we call overweight vehicles, when they're crossing the current bridge, they have to wait until there's no other traffic on the bridge and they cross on the centre line of the bridge. Once the new bridge is in place, they'll just flow across the bridge like any other vehicle. They'll stay in their lane, they can cross at the same time as other traffic.

The current bridge is kind of iconic in the community and on the Alaska Highway. Will the new one still be a closed kind of bridge?

No, it will look a little different. The old bridge was built 70 years ago, so designs have changed.

You're working closely with the Teslin Tlingit Council. Tell us about that relationship.

We have a very close working relationship with Teslin Tlingit Council on this project. Those conversations started a long time ago as this project started in the planning phase, and we've continued those now that we're in construction.

We meet with them on a biweekly basis, so I was down in the community yesterday. Our whole project team goes and meets with representatives from TTC.

We also have a technical working group with them that has representatives from the Yukon government, Teslin Tlingit Council and the contractor, and they meet weekly just looking at environmental issues or having discussions about the environmental aspect of the construction and making sure that we're all working together on that front.

What has been done, as far as the fish and wildlife habitat, to make sure that they're not impacted?

In the planning stage, we had studies done that went out and did an assessment of the wildlife in the project area as well as the wildlife habitat in that project area. From that study, we were able to create what's called a fish offsetting plan. So as we go through construction, we're going to be creating new fish habitat but also restoring and improving existing fish habitat that might be affected by construction.

We're using some really interesting technologies to monitor and protect fish during construction activity. So we do hydro-acoustical sound monitoring in the water so that we understand how the construction noise is impacting the fish. We use something called a bubble curtain — the contractor is using that when they're working in the water. They basically set up a wall of bubbles around the work area and that scares fish away.

And we're doing frequent sampling and testing to ensure that water quality is being monitored.

Tell us about the art aspect of this bridge.

That's an initiative largely being led by Teslin Tlingit Council. I know that at this point they do have a call to artists out. They'll be engaging an artist that will create artwork that can be placed on or around the bridge.

Where the Yukon government comes into that, obviously it's our bridge, so we have to work with them to co-ordinate how that installation happens. We also have our design engineers looking at the proposed designs and just ensuring that what's being installed doesn't impact the structural integrity of the bridge — things like impacting the wind.

Once they land on their artist and the design, we'll do the engineering assessment of how it works. And then installation will happen near the end of the project.

Where are we at, as far as the project goes?

We're now going into the second summer of construction and the contractor is currently doing a lot of work on-site with creating that temporary bridge we were talking about, but also starting to put in some of the permanent piles. So this summer, a big focus will be getting that temporary bridge fully constructed and also putting in temporary pile work and starting to work on some of the piers.

That's the work that's really obvious when you drive through the community. They're also doing a lot of work in terms of developing two different quarry sites that will supply the aggregate material that's required for building the approaches to the bridge.

How many years will it take to build?
The project started last summer and it's expected to be done in 2026.

And we're on schedule at this point?

We are.