Nashville puts a price on rock tunnelling — and our estimate stays more conservative.

The question we are asked most often is also the most legitimate: where do your boring costs come from? Until recently, the honest answer was "from a target The Boring Company is aiming at, but has not yet hit in rock." That is no longer quite true. In Nashville, there is now a real job site, in real rock, with a real price. And it lands squarely inside the geological window that concerns us.

The Nashville figure

On February 25, 2026, a few hours after receiving joint clearance from the State of Tennessee and federal authorities, The Boring Company put its Prufrock tunnel-boring machine into the ground for the Music City Loop — an underground network of about 13 miles linking downtown Nashville to the international airport (BNA). The company says it can build all 13 miles of these twin tunnels for an amount between US$240 and $300 million, entirely privately funded. The first segment is targeting an opening as early as the end of 2026.

Let us translate that amount into a price per mile, the only way to compare it with ours. The 13 miles describe the route; since the system has two one-way tubes, that represents close to 26 miles of tunnel actually bored. Relating the cost to the length effectively dug:

There is the benchmark: around US$9 to $11.5M per mile of tube for boring in rock, announced on a job site under way. Let us keep it in mind.

Why Nashville is our best anchor point

Not all of The Boring Company's showcases are equal. The Vegas Loop, the best known, is dug in soft ground — sands and alluvium — which says nothing about how a boring machine behaves in stone. Nashville, by contrast, is being dug in Ordovician limestone, a competent sedimentary rock. And the Ordovician is precisely the age of Québec's bedrock.

We spelled out the nuance on our geology page: Nashville does not "prove" Québec, but it validates the boring machine in a rock of our geological family. Better still: our dominant rock, the Lévis shale, does not even have the karst problem (those cavities in soluble limestone) that worries Nashville's geologists. Our own Québec challenge, the Logan Fault, is ancient, inactive and already mapped. In other words, this job site is the best available mirror — and our situation is not the harder of the two.

Where our estimate sits

Here is the point that matters for anyone doubting our figures: our realistic scenario does not use The Boring Company's price. It uses a higher price. Our reference rate is US$15M per bored mile (i.e. ≈ CA$12.9M per kilometre), obtained by marking up by 50% the rate TBC is aiming at in soft ground, to account for rock. Let us set the three benchmarks side by side:

Our estimate therefore sits 30 to 65% above the price The Boring Company is announcing today in limestone of the same age as ours — while remaining two to three times below the price of a small conventional tunnel. That is exactly the definition of a well-placed central scenario: neither Elon Musk's sale price, nor the price of the status quo. When you read that the project aims to be "conservative," this is what it means, with the numbers to back it.

The bet, without hiding it

The 30 to 65% gap is our cushion. Is it enough? Two risks deserve to be named frankly.

The execution risk. That is the "announced price vs delivered price" already mentioned. If the Prufrocks never reach, in rock, the costs they are aiming at, our real rate climbs. That is precisely why the dossier presents a range, not a firm bid.

The Québec delivery premium. This one, too, has to be said: the Nashville price is that of a private job site, in Tennessee. Transposed into a Québec public framework — regulated labour, winter, environmental assessment (BAPE), public tenders — it could swell for reasons that have nothing to do with geology. The Québec tramway, at $305M per kilometre, is a reminder that the institutional context has a price. Our only multiplier above the TBC rate is geological; there may be another, institutional one missing, even a modest one. We prefer to write it than to leave it unsaid.

Why the project holds up, even if the bet fails

And here is the argument that matters most: the project's financial architecture does not need the bet to succeed. The "tunnels" line weighs only ≈ $1.9B out of a realistic total of ≈ $12.6B — about 15%. If the real rate doubles, we slide toward the higher scenarios of the dossier, and the cost per kilometre stays in a category of its own:

Even in the worst case — the one where The Boring Company's "magic" does not work at all and we pay the full conventional rate — the network stays two to eight times cheaper per kilometre than the region's other major transport projects. That is what our Other supplier page tests in detail. And before committing the 150 km, a 15 km Phase 1 would measure the real costs under Québec conditions: we price for real, then we decide.

That is the whole difference between an optimistic figure and a robust dossier. The central figure is a bet — calibrated, but a bet. The dossier, for its part, holds up in every scenario. And since Nashville, that bet rests on a machine that is digging, not on a promise.