The Eglinton Crosstown LRT is so long overdue that tunnelling for the line's extension has already progressed over five kilometres, an impressive feat of engineering that is hardly getting the attention it deserves, overshadowed by its problematic sibling.

The Eglinton Crosstown West Extension is adding 9.2 km of new track and seven stations between the existing Crosstown terminus at Mount Dennis and Renforth Drive, with the potential to extend it further west to Pearson Airport and add three stops in the future.

Metrolinx recently offered a rare look below street level for a glimpse at the ongoing tunnelling works for the extension, which have now extended beyond the tunnels' halfway point since launched almost two years ago.

Dig dig dig! Watch how gigantic machines create tunnels to expand the transit network across the GTHA. This video shows the tunnel underway for @EglintonWestEXT. 🚈 pic.twitter.com/eujptBtkHs

— Metrolinx (@Metrolinx) February 22, 2024

Tunnels for the extension are being carved out by a pair of tunnel boring machines (TBMs) manufactured in Germany and shipped to Toronto for the job.

These massive titans of engineering are fronted by rotating cutter heads under immense hydraulic pressure, which dig into the ground ahead, spitting out excavated material which is then removed through the mouth of the tunnel.

The video offers a close-up view of the large teeth that line these cutter heads and chew into rock and soil to etch out the tunnels.

But the TBMs do much more than just dig. They also construct the physical tunnel as they progress forward at a rate of up to 15 metres per day. A component of the TBMs known as a segment erector installs prefabricated concrete tunnel liner segments that form the tunnel walls.

Once segments are in place, concrete is grouted in behind the rings to form the tunnels' cylindrical shape. Segments are then moved forward hydraulically and the process is repeated over and over to form new lengths of walls for the excavated tunnels.

The large launch shaft at Renforth and Eglinton, where the TBMs began their journey in April 2022, is now used as an access point for crews and equipment, while also serving as a terminal for excavated material being removed from the tunnel dig.

However, with TBMs — dubbed Rexy and Renny in a naming competition — now over five kilometres along in their tunnelling job, it would be quite the hike from the launch site to the tunnel's head, currently just west of Royal York and Eglinton.

A vehicle purpose-built for these tunnels shuttles workers and equipment to and from the excavation point as the massive TBMs snake their way eastward to eventually connect with the existing western terminus of the Eglinton Crosstown — combining to form a single line.

The yet-to-be-excavated last leg of these tunnels recently generated anger when it was revealed that Metrolinx and Infrastructure Ontario had agreed to pay a staggering $255 million to construct just 500 metres of transit tunnels covering about half the length between the adjacent Jane Street and Mount Dennis stops.

Ontario awards $255 million contract to build just 500 metres of transit tunnelhttps://t.co/sV5zuM4FFi

— blogTO (@blogTO) February 17, 2024

Rexy and Renny are just two of the three TBMs forging new transit projects in Toronto right now. The Scarborough Subway Extension project is being constructed with an even larger machine dubbed Diggy Scardust, which is forming the widest-diameter subway tunnel in all of Canada.