2023 Travel footprint

23 Feb 2024

Following the work advertised in the previous post, about the carbon footprint of conference traveling, I decided to estimate my own work-related travel footprint for 2023. I have no precise expectation for this, I just want to get an idea of that number, and compare it with other scenarios, to see what makes a difference and what does not.

List of trips

Here is the list of travels I made in 2023 for work. All were round trips from Lyon.

• Paris (three times) by TGV (fast train), which is the transportation choice that almost everybody would make (except PSG football players, maybe).
• Grenoble, a nearby city, by TER (regional train), again the natural choice.
• Prague, for HALG 2023, by long-distance bus. I wanted to avoid flying, and train routes had too many connections to be reliable, so I took this opportunity to try buses.
• Pisa, for SAND 2023, with a mix of fast and regional trains.
• L’Aquila in Italy (that I will approximate by Rome), for DISC 2023, again by long-distance bus. This was planned to be by train, but there were rockslides on the rails in the Alps.

I’ll discuss the bus option at the end of this post.

Computation

For this post, I don’t want to spend too much time fiddling with precise carbon emissions and precise connections, hence I will simply use the following estimates (from this webpage):

• 3.5 gCO2e/km/traveler for TGV,
• 30 gCO2e/km/traveler for regional trains,
• 30 gCO2e/km/traveler for long distance bus,
• 260 gCO2e/km/traveler for plane.

Also I use the road distance for train and bus, and the straight line distance for plane.

Two remarks here. First, the fast trains are extremely cheap in carbon in France (my three trips to Paris weight the same as my trip to Grenoble!). This is because electricity in France is mainly from nuclear plants, and also because TGVs have a lot of passengers, and have benefited from massive investments. Second, I was surprised to learn that long-distance buses are just as good as regional trains. Intuitively a bus looks more like a car than a train, and is also smaller, so I would have guessed they emit more.

Results

The following chart shows how much carbon is emitted for different scenarios: the one I did with trains and buses, the one where buses are replaced by planes, the one where all trips abroad are by plane, and finally one where I would have made just one trip: going to PODC 2023 in Orlando.

A few take-aways from this: opting out of attending PODC had a greater impact than abstaining from air travel for other trips, yet choosing buses over planes still had a significant effect. Remember that a reasonable carbon budget for one person per year is 1500kg (including both work-related and personal emissions).

About long-distance buses

Long-distance buses are not a commonly chosen mode of transportation for attending conferences. They aren’t even included as an option in the software my employer uses for planing trips. In some ways, buses combine the drawbacks of both planes and trains: the journeys are uncomfortable and time-consuming. The only thing that is convenient is that often one does not need (many) connections.

If someone were to consider, ‘Should I take a plane or a bus to get to conference X?’ the prospect of spending 10 hours in close proximity to a stranger and making frequent stops at bus stations would likely be discouraging.

However, let’s consider this from a different perspective: if I aim to keep my carbon emissions below a certain threshold and I’m contemplating attending conference X, then the only viable option might be taking a bus. Do I still want to go? In a way, the bus option broadens our possibilities within a given carbon budget.

(Side note: I used chat-GPT to improve some sentences here, which is why it might sound like my English suddendly improved!)