The environmental case for a railway is usually made with one number: the carbon saved by taking people out of cars and planes. That number matters, and we deal with it first. But the bigger environmental fact about a railway is decided before a single train runs — by where the line is put.

A route that follows an existing transport corridor inherits ground that has already been cleared, drained, fenced and cut through. A route driven across open country creates a new line of disturbance where there was none. The same choice governs the human side: whether a project takes its land from beside a highway people already live next to, or from farms and communities that never expected a railway.

This page covers the four consequences that follow from that one decision. On each of them the two routes differ not by a margin but in kind.

Over fifty years the brownfield route is a net removal of carbon. The greenfield route, measured the same way, is a net emitter. Not smaller — opposite.

Three things drive that. Construction carbon is the one-off emission of building the line. Building at grade beside an existing highway needs no tunnelling through the Canadian Shield, no deep cuts, and no treatment of the unstable marine clay south of Ottawa. Our estimate is 4.9 Mt for the brownfield line against 14.9 Mt for the greenfield one — roughly three times more.

Running the trains turns out to be almost a rounding error either way. On Ontario’s grid, electric traction at 200 km/h emits about 6 grams of carbon per passenger-kilometre.

Freight is what decides it. A passenger line built beside the existing freight railway frees capacity on that railway. Every long-haul truck that moves off Highway 401 onto rail saves about a quarter of a tonne of carbon on a typical haul. At 3,000 trucks a day — about eight freight trains — that is roughly 13.5 Mt over fifty years. The greenfield route has no freight function, so it cannot claim any of it.

That shows up most clearly in how long each takes to pay back its construction carbon. The brownfield line breaks even in 12 to 18 years and stays in credit after that, and the timing barely changes with passenger numbers because freight carries it. The greenfield line depends entirely on passengers: about 22 years at the ridership its reference class suggests, 39 years at a more central figure, and at low ridership it does not break even within fifty years at all.

A railway is a barrier to animals. Where you put the barrier decides whether it cuts through habitat that is still whole, or adds one more strand to ground that is already crossed by a highway and a freight line.

The greenfield alignment runs through or beside three of eastern Ontario’s most sensitive landscapes.

The Frontenac Arch

A billion-year-old granite ridge linking the Canadian Shield to the Adirondacks, a UNESCO Biosphere Reserve since 2002, and the narrowest point on the wildlife corridor running from Algonquin to the Adirondacks. It holds Blanding’s turtle, the grey ratsnake, the eastern whip-poor-will and somewhere between half and two thirds of Canada’s cerulean warblers, along with fisher, black bear, moose and eastern wolf.

Because it is already the tightest pinch-point in a continental corridor, a new barrier laid across it does disproportionate harm. It does not just disturb habitat; it narrows the last gap animals still move through.

The Napanee Limestone Plain

Alvar — flat limestone pavement with almost no soil, flooded in spring and parched in summer. It exists in only two places on Earth, the Great Lakes basin and the Baltic, and about 85 per cent of North America’s alvar is in Ontario. It supports part of Ontario’s remaining eastern loggerhead shrike population, a bird now down to a handful of nesting pairs province-wide.

We say that plainly because it matters. The corridor audit in Chapter 4 finds the brownfield spine still crosses about 41 per cent natural cover. It is not a route through nothing. It is a route through ground that a four-lane highway and a Class I freight main already run down.

A 479-kilometre construction site has to be fed. The brownfield spine needs roughly 9.8 million tonnes of fill, ballast, track and concrete — about 20,400 tonnes for every kilometre built. Delivered entirely by road, that is around 390,000 loaded truck trips, running on the same Highway 401 the railway is being built beside, during the decade that highway is itself being widened.

Britain has already run this experiment. HS2 moved more than 10 million tonnes of material by rail, and the reason it did is the instructive part: it was not a carbon measure. Local councils refused the lorry routes the project had planned. Moving material by train was how the works stayed consented.

And this is not a strategy a project can simply decide to adopt. It is a property of where the line is. A route beside an existing freight railway has yards at Belleville, Kingston, Brockville, Cornwall and Coteau available as railheads, and on the Ottawa legs runs on publicly owned track. A greenfield route through the Frontenac Arch has no railway to deliver to. Materials arrive by road on haul roads built for the purpose, and excavated rock leaves the same way, through the same rural communities.

We score this two ways. The Latent Friction Index measures the structural friction a route will generate, before any opposition has appeared. The Community Friction Index measures opposition that has actually materialised. On the forward measure the brownfield spine scores about 29 and the greenfield corridor about 65. On the realised measure the greenfield project has already reached 54, and is rising.

This is not only a political point. In our reference-class cost model, community friction is a statistically significant predictor of cost escalation — it carries most of the explanatory power in what a kilometre actually costs to build, across the international sample. The friction a new corridor generates gets priced into the bill.

The difference comes down to where the land is taken from. Both routes need new land; a railway cannot be laid inside a live highway. But land taken beside an existing highway and freight line is already fragmented, already severed, and already next to infrastructure. Land taken across open country is none of those things, and the people it is taken from had no prior relationship with the project.

One thing that cuts the other way

The margin beside Highway 401 that makes the brownfield route cheap is being consumed — by interchange development, logistics parks moving east, subdivisions at growth centres and utility lock-in. Chapter 4 puts the cost of waiting until the corridor fills in at around $20 billion, which would roughly halve the route’s benefit-cost ratio and erase the advantage that is the reason to prefer it.

The brownfield option is the low-friction one, but only while the window is open.

Everything above treats the corridor as something done to the land it crosses. There is a reciprocal question worth asking.

Against the intuition that Ontario’s sun improves as you go south and west, the province’s strongest solar yields are in the east. Kingston records about 1,194 kilowatt-hours per installed kilowatt per year and Ottawa about 1,140, against roughly 1,096 for Toronto and 1,084 for London. The railway is proposed through the sunniest ground in southern Ontario — and developers noticed first. Four ten-megawatt solar farms stand within a few kilometres of the 401 around Ingleside alone — Rutley, Cornwall, David Brown and South Stormont, built between 2012 and 2015 — and at Edwardsburgh Cardinal a partnership including the Algonquins of Pikwàkanagàn First Nation is building the largest battery storage system in Canada.

This matters for a reason that has nothing to do with electricity. A right-of-way takes a strip of land and pays for it once. A generation lease pays on the land that remains, every year, for decades. The awkward leftover parcels created by a railway are poor ground for crops and perfectly good ground for solar panels. The Rutley farm gives a sense of the scale: ten megawatts across about ninety acres.

The limits deserve stating as plainly as the opportunity. Solar output peaks in summer and stops at night, while a railway’s demand is flat and year-round — so this is a commercial and community proposition, not a way to power trains. Provincial policy restricts ground-mount solar on prime farmland. Connection capacity governs what can actually be built. None of that is a reason to leave it unexamined; it is a reason to examine it while the route is still being decided, rather than after the land has been taken and the relationships have set.