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Rails, ballast, gravel pits, overhead wires, train stations… Even though trains emit up to 80 times less CO2 than airplanes in France, they’re not without their environmental impact. Rails and infrastructure consume sand, gravel, and steel, and result in land being converted to non-natural uses. This is precisely what Benjamin explored in an episode of our podcast by welcoming Philippe Bihouix, an engineer by training, who spent about ten years heading up SNCF Fret’s European operations and who now leads AREP, the SNCF Group’s leading architecture firm. He is also a recognized authority on resource management and low-tech solutions, and co-author of the book The Stationary City (Actes Sud, 2022) with Sophie Jeantet and Clémence de Selva. In short, a rare combination of expertise in railway engineering and the philosophy of simplicity, offering a candid answer to a counterintuitive question: Should trains, too, go low-tech?
In The Stationary City: How Can We Put an End to Urban Sprawl? (Actes Sud, 2022) Philippe Bihouix sets out to zero net land conversion (ZAN), as set forth in the Climate and Resilience Act of August 22, 2021: to halve the rate of consumption of natural, agricultural, and forested areas by 2031, with the goal of achieving zero land conversion by 2050.
He points out a structural limitation of the model: unlike carbon, whose sinks can absorb emissions for millions of years, there is no equivalent stock of land that can be “de-seized” indefinitely to offset new construction. Housing alone accounts for approximately 60% of land conversion in France (a figure confirmed by reports from Cerema and the Senate on the subject).
On the ground, however, this objective remains controversial. Some rural elected officials, through the Association of Rural Mayors of France, have expressed concern that the ZAN would “put a lid” on thousands of sparsely populated municipalities that already make minimal use of land. Parliament ultimately relaxed the provisions with the law of July 20, 2023, which establishes a “rural guarantee” of at least one hectare of buildable land per municipality through 2031, proof that land-use restraint, however necessary it may be, is difficult to negotiate on a region-by-region basis. Rail projects are no exception: the future Bordeaux-Toulouse high-speed rail line, for example, would alone result in the development of approximately 5,000 hectares—the equivalent of half the area of inner Paris.
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Hence the idea of residential town, a phrase borrowed from the 19th-century economist John Stuart Mill: a city that stops spreading out but continues to transform itself.
“This concept of a ‘stationary city’ would not prevent cities from making urban progress—and thus from revitalizing themselves, transforming themselves, adapting to climate change, adapting to an aging population, adapting to new uses, improving energy efficiency, and so on.” —Philippe Bihouix
Among the concrete measures mentioned: the rehabilitation, even though France has about 3 million vacant housing units, of which just over 1 million have been empty for more than two years (INSEE), while several million others are underoccupied by aging households living in homes that have become too large. Opening one’s home to a student or participating in intergenerational housing thus becomes a way to provide housing without developing a single additional square meter of land.
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That's the crux of the matter for us: Is rail really more environmentally friendly than air travel when you consider land use and material consumption? Philippe Bihouix's response is more nuanced than one might think. " If we were to take the train based on the number of kilometers traveled, he explains, "It is less efficient in terms of material consumption than an airplane."
The explanation: An airplane flies 15 to 18 hours a day, carries many passengers, and requires no linear infrastructure—only isolated runways. Trains, on the other hand, constantly tie up tracks, ballast, and open gravel and sand pits to produce the necessary materials—which are visible along many rail lines in the form of bodies of water.
But thinking "per kilometer traveled" is a classic bias, similar to the one found in debates about transportation safety. What matters is the actual distance : For the same trip (vacation, family visit), flying inherently involves traveling far more kilometers than taking the train, and it also comes with an “ecological footprint” due to its high level of electrification.
Added to this is a factor that a simple comparison overlooks: a rail line pays for itself over decades. France’s first high-speed rail line, the Paris-Lyon line, has been in operation since 1981—more than 40 years—and continues to carry millions of passengers each year. When viewed in light of this lifespan, the initial capital cost of rail becomes increasingly insignificant compared to the CO2 savings it delivers, trip after trip, year after year.
Once the comparison is reframed in this way, the material advantage of air travel virtually disappears, and what remains must be viewed primarily in light of a benefit that air travel itself can never offer: up to 80 times less CO2 per trip, over the infrastructure’s lifetime.
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On the issue of fuel, Philippe Bihouix also points out that the argument often put forward by aviation advocates (“once the energy problem is solved, air travel will be more efficient than rail travel”) remains largely hypothetical: in early 2025, Airbus announced that it was delaying the entry into service of its hydrogen-powered ZEROe aircraft—originally scheduled for 2035—by 5 to 10 years, and reduced the program’s budget by 25%. In short, the “clean” aircraft presented as an alternative remains, for now, a promise with no reliable timeline.
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Another important point to note: not all train trips automatically replace a trip by plane or car. Philippe Bihouix identifies three effects that occur simultaneously:
With regard to OUIGO in particular, he highlights the benefits from a resource optimization perspective: existing trains running more frequently, maintenance slots better utilized, and no need to manufacture new dining cars.
Does the train really need to go low-tech?
To answer this question, Philippe Bihouix begins by dispelling a false debate—that of in-flight Wi-Fi. While an in-flight connection may seem indispensable today, it is above all a result of offset of reference points (a concept borrowed from biologist Daniel Pauly): A few years ago, Wi-Fi worked much worse on TGV trains, and passengers simply worked differently—offline.
"It's because, as consumers, we've all gotten used to having that little something extra, so when it's taken away from us, it's unpleasant." — Philippe Bihouix
On the substance of the matter, he is categorical: the train today is “an ultra-high-tech system.” Between the signaling system, the overhead wire, pantograph wear, and the synchronization of trains traveling at 300 km/h with a braking distance of around 5 km, the complexity is very real, and, in his view, incomparable to that of aviation, due to the constant interaction between the track, the overhead wire, and the moving vehicle. At AREP, the agency he heads, the team has, for example, worked on the design of the TGV M—the new generation of TGV trains—alongside a Japanese design studio, proof that this system, as complex as it may be, continues to evolve.
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But low-tech solutions do indeed exist, particularly for serving remote areas. Today, a conventional railroad track is designed to support up to 22.5 metric tons per axle, while a TGV weighs approximately 400 metric tons. Philippe Bihouix mentions ongoing discussions—at SNCF Voyageurs as well as elsewhere—regarding lighter trains that travel at lower speeds (50 to 70 km/h), on tracks requiring less intensive maintenance, carrying less complex equipment, and stopping at simpler stations—or even, eventually, with on-demand stops, as is already the practice on certain bus routes.
Issue du monde de la communication et des médias, Sophie est Responsable éditoriale chez HOURRAIL ! depuis août 2024. Elle est notamment derrière le contenu éditorial du site ainsi que La Locomissive (de l'inspiration voyage bas carbone et des bons plans, un jeudi sur deux, gratuitement dans ta boîte mail !).
Convaincue que les changements d’habitude passent par la transformation de nos imaginaires, elle s’attache à montrer qu’il est possible de voyager autrement, de manière plus consciente, plus lente et plus joyeuse. Son objectif : rendre le slow travel accessible à toutes et tous, à travers des astuces, des décryptages et surtout, de nouveaux récits.
