The Minnesota Zoo in Apple Valley stretches over 500 acres, has large animal habitats, educational exhibits and a natural hardwood forest that it winds through, along with a 1979 monorail that was decommissioned in 2013 and wasn’t serving anyone until it became a new attraction, thanks to contractor PCL Construction, architect Snow Kreilich Architects and landscape architect TEN x TEN.

The $39-million investment to add the Minnesota Zoo Treetop Trail to the zoo was minimal considering it could use all of the old supports from the elevated train. SKA designed the world’s longest elevated pedestrian treetop loop (1.25 miles) to make the old train into a walkable trail above the zoo. Built on the old railway track, the path is at least 8 ft wide its entire length but it has 22 bump-outs that extend its width to 14 ft in some places. The project adds 70,000 sq ft of new space to the zoo that PCL built entirely at height.

Photo by Corey Gaffer, Corey Gaffer Photography

PCL used a phased approach, dividing the trail into four sequences to maximize efficiency. This approach considered the zoo animals’ daily routines, supply availability and crane locations to avoid obstacles during construction.

What followed was a process that used the train rail itself as a materials handling platform with a tractor on bogey wheels used to deliver the prefabricated major sections at ground level, which then allowed for simpler installation 32 ft into the air where the trail overlooks the zoo.

“We designed it so that we could fabricate the whole system in 20-ft-long modules,” says Michael Osowski, senior project manager for PCL. “That was all the framing and everything. It was fabricated, assembled and then shipped out to the jobsite in these 20-foot sections and then we were able to install the handrail on the ground, and so that was completely safe. We craned that section up onto the trail, and then we were able to push it off into its final resting location.”

Photo by Corey Gaffer, Corey Gaffer Photography

Osowski said once the decking was on, then electrical and lighting and other trades could do their work in a much safer manner than if it was all stick-built.

The design of the trolley system on the existing track featured a rubber-wheeled subcompact diesel tractor, a custom-built guidance system and a safety enclosure with an access platform and canopy. The tractor’s wheels rode on the beam, driving the trolley, while guides ensured it stayed on track. The guide system relied on hydraulic power, which enabled it to be raised off the trail for ground driving and movement between access points.

It moved up to 30,000 lb, pulled scaffolding, transported workers and pushed sections of trail to their final locations. For snow removal, during the winter months, PCL attached a 16-in. ATV snowplow to the front of the trolley, making the process more efficient and ensuring the trail remained accessible

Another uniquely Minnesota answer to working during record snowfall in 2022 was using ice fishing sheds placed on the trail’s wider section to provide warmth for up to four trade workers at a time.

“You can get an ice house, these pop-ups that are basically 18 feet wide that fit perfectly on the trail, then they were easy to move,” Osowski says.