Impacts on the environment, Calgary parks and area connectivity are primary considerations for the type of bridge that will cross the Bow River as part of the Green Line LRT project.
Last week, the city met with bridge architects to examine the bridge types that were suited for the major crossing, looking at how they each interact with the area around them.
Four bridge types were discussed, and these will be presented for feedback during Green Line LRT open houses this week.
Graham Gerylo, senior manager of planning for the Green Line project, said they’re hoping the citizen feedback will help guide the specific design decisions moving forward.
“These are actually conversations that we want to have with Calgarians as we move forward with leading the planning design process on the bridge to understand where the priorities also may lay with Calgarians,” he said.
The four bridge types vary in visual appearance, physical impact in a given area and, of course, cost. But, Gerylo said they’re all within the Green Line bridge’s budget envelope.
Here are the four bridge types being considered, each with design elements and how they might impact the surrounding area. NOTE: All photos are artistic renderings, they are not the actual bridge designs.
Constant depth viaduct
This is the simplest structure, Gerylo said, and it has constant spacing between the support piers, repeated for the course of the bridge structure. This version limits the visual prominence of the bridge itself as it blends into the city along the horizon.
Still low key, the trestle bridge, has v-shaped piers and there can be more distance between them.
“So, it’s a way of actually using the pier to manage some of the potential environmental footprint of the bridge,” Gerylo said.
Tied Arch bridge
Gerylo said this has many of the same features as the constant depth viaduct, but the arch support allows for it to span longer distances over the river.
“You can use different spans to create some of the distance between the concrete piers,” he said.
“(Spans) allow you to avoid potentially sensitive areas like the river channel itself or a wetland.”
This bridge type also brings in greater visual prominence to the structure.
Cable stayed bridge
The cable stayed bridge is “more pronounced architecturally,” said Gerylo and the cables help support the longer spans, meaning fewer piers touching the ground.
Designs important for feedback
Earlier this year, Coun. Druh Farrell expressed concern about the impact the new alignment would have on Prince’s Island Park. Further, the impact on connectivity in the area around the River Walk.
“Prince’s Island is the jewel in the crown of our whole park system,” Farrell said in an interview at the end of January, just after the new Green Line alignment was delivered.
“The last thing we want to do, the last thing I want to see, is us damage our most precious park space.”
Farrell said it all depends on the details.
Gerylo said that’s where the feedback comes in. They want to gauge the priorities of Calgarians in and around Prince’s Island and the Bow River.
Each bridge type presents different opportunities and challenges – some reduce encroachment on the potential park space, but have a much greater visual impact.
“So we’re looking at the different types to understand the visual prominence, but also as a way of helping us as a team understand, how could the bridge over the river interface with Prince’s Island and the Bow River,” Gerylo said.
“It’s a way to start understanding the trade offs visually, environmentally and from even a park or river user perspective.”
Other bridge aspects to consider
Connectivity is another priority area for the Green Line team. There’s worry the Green Line path will disrupt the flow of traffic along the River Walk.
Gerylo said it’s part of the feedback they’re hoping to get from citizens. They recognize the need to keep the continuity and connectivity of the existing network.
But, they’re also looking at how they can add to it. Should feedback tell them a multi-use pathway is needed on the bridge to continue the flow of multi-modal traffic, it’s something they could integrate into a final plan.
That influences the bridge design and its visual appearance.
Creating an urban design strategy will play a role in this as well. Given it’s going through a natural habitat they want it to blend in.
“We want to still bring, whatever the design or form is that we choose, how do we something that still is interesting, that blends into the environment, that brings us some are interesting urban design elements, whether that’s lighting or textures or whatever ideas that we hear from Calgarians,” said Gerylo.
Next steps for the bridge
Once city council determines the final alignment at the end of April, they’ll start to get serious about bridge design.
Gerylo said their final design will be about finding a balance; minimizing the bridge’s footprint in both the aquatic and park habitats, but also ensure it meets the priorities of Calgarians.
They’ve got six key objectives they’re hoping to meet focused on flexibility, functionality, connectivity and mobility and environmental impact.
After this, they do have the requisite environmental and permitting process to wade through – particularly around the fisheries and the impact the bridge might have on the Bow River waterway.
Citizens can hear and see more about these bridge options at city open houses going on March 4, 5, 7 and 8.