North-West PATH Tunnel

Solving a 3D puzzle

City of Toronto | Canada | 2010–2017

65 m
cut-and-cover tunnel complete (Phase 1)

World's largest
pedestrian tunnel network

different Toronto utilities relocated

Willis Chipman Award
Consulting Engineers of Ontario - 2016


  • More people pass through Union Station every day than through Toronto’s international airport, and that number is expected to double by 2020.
  • The PATH tunnel connection on the east side of Union Station was severely congested, prompting the need for a tunnel on the west side as a passenger relief valve.
  • Project was adjacent to two concurrent large construction projects and surrounded by heritage buildings.
  • Water mains, sewers, gas mains, fiber optics, underground hydro transmission and distribution circuits, overhead and underground street lighting, traffic control systems, and steam heating networks all needed to be relocated.
  • All of Canada’s major financial institutions depend on these power and fiber-optic connections.


  • Complex 3D models were developed for multiple custom tunnel alignments and utility relocation options.
  • Digital construction prototypes in the context of existing conditions allowed full visibility of the utility or structural conflicts.
  • Designed custom solutions for unique utility relocations, including for a sewer whose existing profile went directly through the proposed tunnel.
    • Designed a siphon, made of 6-millimetre-thick stainless steel, directly between the new tunnel’s floor slab and the existing subway’s roof slab.
    • With insufficient space to accommodate a circular sewer, we designed transitions from a circular cross section to a rectangular equivalent cross section and back again, with only 50 mm clearance between the siphon and the structure.
    • Built directly on top of the existing subway system in an extremely congested construction area.


  • 2016 Willis Chipman Award, Consulting Engineers of Ontario.
  • 2016 Award of Honor, American Council of Engineering Companies – New Jersey Chapter.
  • Extensive 3D modeling and approval efforts were needed to communicate the scale of complexity to each of the 12 utility owners.
  • Contract drawings for construction, detailed plans, elevations, and cross sections were generated directly from the 3D model.
  • Also constructed two signature surface buildings.

Project numbers

25 utilities relocated
65 m of tunnel
2 surface buildings constructed

What's your challenge?