Best Specialty Construction: Minnesota Zoo Treetop Trail

The Minnesota Zoo’s overhead monorail was decommissioned in 2013, but the rails installed in 1979 remained as a relic of a bygone era of overhead transportation—until BARR Engineering and Snow Kreilich Architects reimagined the route as the Treetop Trail.

SKA designed the world’s longest elevated pedestrian treetop loop (1.25 miles) to transform the former monorail system into a walkable trail. The path is at least 8 ft wide for its entire length but 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, which PCL installed at height.

Photo courtesy of Corey Gaffer, Corey Gaffer Photography

“When it comes to anytime that we work above six feet—it doesn’t matter if it’s six ft or sixty feet in the air—we require full body harnesses and tie offs when we’re working that high above the ground,” says Michael Osowski, senior project manager for PCL. However, a kit of parts approach using pre-fabricated trail modules enabled crew members to work at height without the need for tie-offs.

“[Modules included] all the framing and everything.” Osowski says, and were “fabricated, assembled and then shipped out to the job site in these 20-feet sections and we were able to install the handrail on the ground, so that was completely safe.”

The Minnesota Zoo’s Treetop Trail gives visitors a view of most of the 500-acre zoo.
Photo courtesy of Corey Gaffer, Corey Gaffer Photography

The sections were craned into the sky, and then PCL crews were able to position them into their final resting location and connect them to the existing steel frame of the monorail’s rails. Once decking was placed, electrical, lighting and other trades could do their work in a much safer manner. A rubber-wheeled, subcompact tractor—capable of moving up to 30,000 lb—was built on the existing rails to help with material deliveries, worker transport, pushing sections into place and other tasks.

PCL used a phased approach, dividing the trail into four sequences to maximize efficiency, sequence construction, consider the zoo animals’ daily routines and avoid obstacles.