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Ford says the tunnel would span º£½ÇÉçÇø¹ÙÍøand extend west to Brampton but has offered few other details, saying his party is awaiting a feasibility study to know the potential cost and construction timeline. What Ford says he does know is that drivers like the idea.

“The easiest way to know if someone commutes on the 401, ask them what they think about building a tunnel,” Ford said recently.

“These hard-working families, they just want to get to work, get to soccer practice after work, get home, without the headache of bumper-to-bumper traffic from one end of the 401 to the other.”

Liberal Leader Bonnie Crombie, at Monday night’s leader debate, launched a blistering attack on what she called “a fantasy project” that will take 40 years to build, do nothing to alleviate congestion and, she said, “bankrupt the province.”

Some observers think the estimated tunnel cost could be as much $120 billion, which would gobble so much of the province’s capital budget that it would be a non-starter.

Sometimes, politically, it doesn’t matter. John Tory campaigned for mayor of º£½ÇÉçÇø¹ÙÍøin 2014 promising SmartTrack, a “surface subway” using existing rail line, that engaged voters and helped him get elected — but now barely exists.

The Star asked three transit experts — Shoshanna Saxe, a civil engineer and infrastructure expert at U of T; Murtaza Haider, an expert in the economics and cities and regions who is research director of the Urban Analytics Institute; and Matti Siemiatycki, director of the U of T’s Infrastructure Institute — key questions about Ford’s tunnel vision. (Some answers have been edited for brevity and clarity.)

1. Based on what we know, how long do you think such a tunnel would take and how much could it cost?

Saxe: It would take a decade or longer to do ground investigation, design the tunnel and then build it. It’s possible that even if we were really gung-ho about it, it would open in the 2040s. At the moment, it’s a fictional project so there’s a lot of uncertainty. It would cost tens of billions of dollars but you need to plan it out and, at this point, it’s just a thing Doug Ford has talked about.

Haider: The construction of a tunnel spanning 60 kilometres or more — connecting Mississauga and Brampton in the west to Scarborough or beyond in the east — would likely face prohibitive financial and temporal challenges. Preliminary cost estimates for tunnelling in urban environments range from $250 million to over $1 billion per kilometre, though precise figures remain speculative without geotechnical surveys, environmental assessments, and feasibility studies. Timelines for such megaprojects are inherently uncertain … A fully underground tunnel accommodating both automotive and transit traffic could span decades to complete.

Siemiatycki: I wouldn’t even try to estimate this because whatever I say, the tunnel is going to take longer and cost more. You could do an internal cost estimate, where you take all the details of the project and build it bottom up, or you could benchmark it relative to the cost-per-kilometre to build other similar projects around the world. Either way, we’re into the tens of billions of dollars and above. º£½ÇÉçÇø¹ÙÍøis a high-cost jurisdiction — our transit projects are costing $1.5 billion per kilometre.

2. If a tunnel is built under  Highway 401 spanning the city and beyond, would it eventually make car commuting faster and if so by how much?

Saxe: No, it won’t make car commuting faster. For nearly 100 years, we’ve checked if adding road miles speeds up how fast people get to drive. Sometimes it does for a couple of years, but within five years everyone’s back to driving the same speed as before — there’s just more people stuck in traffic. It’s also unclear if Ford wants to build a bypass, where you have to go one end to the other, or with entrances and exits that add congestion because it slows people down. Most people driving that stretch of Highway 401 are stopping somewhere between those 50 kilometres.Ìý

Haider: The proposed tunnel aims to address unmet travel demand generated by decades of population growth and socioeconomic activity that existing road and transit networks cannot fully accommodate. While the tunnel would enhance throughput capacity — moving more people and vehicles during peak periods — its impact on reducing travel times across congested corridors like Highway 401 is expected to be marginal. Capacity expansion should be framed as a mechanism to absorb latent demand (travel not currently realized due to constraints) rather than a solution to congestion. Failure to address latent demand risks exacerbating gridlock and stifling economic productivity.

Siemiatycki: Anyone commuting now — this tunnel project is not going to solve your commute, this is a decades-long project. You will very likely be retired by the time this is completed. That aside, what we’ve found with these big highway projects is that they solve the project in the short term, because they do add capacity, but they shift the bottlenecks to elsewhere in the network.

3. How much disruption would tunnel digging create? Is it possible to dig underneath without impacting traffic on the busy highway above?

Saxe: Technically it is possible to dig with very little interaction at the surface. However, do we want any entrances or exits or air valves? Construction of them would cause disruption and traffic during tunnel construction. Given Ford is talking about building right under Highway 401, I’m guessing there would be a lot of traffic impacts above for a long time.

Haider: A project of this scale would necessitate extensive engineering interventions, including large-scale earth removal, soil disposal, and logistical co-ordination of heavy machinery and labour. Numerous access and egress points would compound disruptions to surface-level traffic and adjacent land uses, potentially persisting throughout the multidecade construction period. Historical precedents, such as Boston’s “Big Dig” — which saw costs escalate from $2 billion to $20 billion — highlight risks of budgetary overruns and scope creep, underscoring the need for cautious fiscal and operational planning.

Siemiatycki: They can tunnel underneath it but, just like with the ongoing subway digging projects, the dirt has to come out somewhere. With a project of this scale there is going to be a huge amount of earth that will need to be trucked away somewhere. All of those trucks create their own traffic and congestion, as well as safety concerns as we’ve seen with Ontario Line trucks. Even if you’re digging underground, it’s never impact-free above.

4. If º£½ÇÉçÇø¹ÙÍøhas multi-billions of dollars to spend on reducing gridlock and commute times, what is the most effective use of those dollars?

Saxe: The absolute most effective thing would be to invest in much better public transit. In the short term, more bus rapid transit (BRT, in dedicated lanes) and many more bike lanes can help reduce gridlock. In the long term, you can invest in more commuter rail transit. Something that wouldn’t cost money, but would reduce gridlock, is better zoning and land-use planning to ensure growing communities are oriented to transit so those residents don’t have to drive everywhere.

Haider: A more pragmatic approach to enhancing regional mobility lies in prioritizing high-capacity bus rapid transit systems. Elevated BRT corridors, operating along Highway 401’s median with articulated buses in platooned formations, could provide dedicated right-of-way at a fraction of tunnelling costs. Such systems could integrate with existing transit networks via underground interchanges or elevated pedestrian bridges, as exemplified by elevated rail-pedestrian linkages in New York City.

Siemiatycki: We are tunnelling now for public transit. Part of the reason projects are expensive here is we try to put many of them underground, in some cases where it’s not the right tool. If I had tens of billions of dollars I would continue to invest in public transit and, as that transit comes online, add road tolls as a way to manage construction. I would also immediately add a bus lane to make commuting that way much quicker. In the leaders’ debate, Doug Ford acknowledged tolls actually work because he talked about the potential impact of taking tolls off Highway 407, that it would get busier.