– Last Update January 20, 2024 –

When it comes to reducing CO2 emissions, some politicians dream of plan A: replace all flights shorter than 750 kilometers with high-speed rail. If that dream were to become a reality, it would be a nightmare for emissions.

Direct emissions

We will first have a look at direct emissions. For trains, the distance has little influence on the emissions per passenger per kilometer (pkm), but the average load factor is important. For HSR that factor is 50%. For reference load factors of 30% have been added , the average for the regular train, and of 70%.

Due to their great flexibility, aircraft have a high and stable load factor of more than 80%, but with aircraft the distance makes a difference. Following an often-made division, we look at destinations that are less than 250 km, from 250 to 500 km, from 500 to 750 km and from 750 to 1500 km removed from Amsterdam. All distances as the crow flies

The average emissions from flights between 500 and 750 km, 90 grams/pkm, turned out to be almost equal to the average of flights between 250 and 500 km, 92 grams/pkm. In the graph they are therefore presented as one:

CO2-emissions in grams per passenger per kilometer (grams/pkm)

HSR clearly performs better than aircraft in terms of direct emissions. But this is only part of the story. The construction of HSR track comes with quite a lot of emissions and you really must factor that in. As we will see the volume of traffic, the number of passengers per year, will then be very important for the emissions per pkm.

Emissions with infrastructure

According to a report by the European Court of Auditors, ECA, the limits for a viable HSR connection are distances of up to 500 km with at least 9 million passengers per year. We start with a million passengers and look no further than 750 km. This is the result for three different traffic volumes:

Emissions including infrastructure and detour factor for three traffic volumes

With at least 50% less emissions aircraft always perform better than HSR with a volume of one million or less passengers per year.

Incidentally, distances less than 250 km are rather unimportant, because at distances of up to 250 km HSR is not the alternative for aircraft, but for cars. Flights from Amsterdam to the destinations Brussels and Düsseldorf, for example, carry almost exclusively network traffic. These passengers start or end a longer journey via the Amsterdam hub. On these routes virtually no local traffic is carried.

Cost per ton avoided

So, for the average load factor of 50% the tipping point for emissions per passenger is three million passengers. However, the costs per ton of emissions avoided at that point are sky-high. Even with ten million passengers they are, at 1,510 euros per ton, still a multiple of the costs of plan B: promotion of the production of bio-kerosene. That plan would cost 316 euros per ton avoided:

Costs per ton of CO2-emissions avoided for a one-way trip of 500 km with three traffic volumes
* Aviation does not calculate fuel by volume but by weight because the energy content of a kilo is always the same. While a warm liter contains less energy than a cold one.

Only with thirty million passengers or more will the costs per avoided ton be lower than that of plan B. You will find such high-volume routes in Japan and perhaps also in China, but not in Europe for the time being.

Plan B wins

Plan B has another advantage. The construction of HSR track can easily take twenty years. The production of bio-kerosene can start next week and will have an immediate effect. Moreover, this will eventually enable all European aviation routes shorter than 750 km to become emission-free. Plan A would be able to replace only a fraction of those routes.

So, the choice between plan A and plan B is not very complicated. There may be good reasons to build an HSR-connection, but reducing emissions is not one of them. That dream is indeed an illusion.

Sources and calculations

The connections with Amsterdam used are the destinations that, according to a study by Royal HaskoningDHV, could be replaced by HSR and which, according to that study, have a potential of at least 400,000 passengers per year. See figure 2.3 in their report.


For aviation, the actual fuel consumption with the actual load factors over the flown distance is used. These data are all available in the public domain, in this case the CO2-calculator on the KLM website, consulted on September 3, 2021.

The contribution of infrastructure to total emissions for aviation is very limited. According to the EU, DG Climate Action (Final Report 09/2012, page 53, figure 7.4) on average 2%, with a maximum of 3%. I calculated with 3%.

HSR operational emissions

Finding the data was a bit more difficult for HSR, but in the end four sources provided relief. For the HSR operational emissions I used an article from 2020 by Milan Janić of TU Delft. With a load factor of 100%, he arrives at 40 grams/pkm and he has calculated with an emission of 546 grams of CO2/kWh for electricity production. These emissions vary quite a bit in Europe, from 56 grams in France to 751 grams in Poland. I have calculated with the European average of 255 gr/kWh and therefore with 19 grams for a 100% load factor and 37 grams for 50%.

HSR costs

The costs of 25 million euros per kilometer are mentioned as average costs in a report by the European Court of Auditors but seem a bit on the low side. The HSR Stuttgart-Munich (267 km) came to 50 million, the HSR South in the Netherlands (117 km) to 62 million and the British HS2 (London-Birmingham, 225 km) were stated in 2011 as 83 million euros per kilometer. According to the 2020 update, the costs of HS2 are now estimated to be 205 million/km.

The difference with the ECA might be the result of the fact that the ECA does not take into account the more expensive tunnels. Why not is not clear, but these do have a major impact on the costs. The first HS2 plan contained 10% tunnels (22 km), the latest version 45% (102 km). Constructing HSR track in a crowded and/or vulnerable environment apparently requires a lot of tunnels. A minimum of 15% might be a reasonable assumption. But to calculate conservatively for HSR I used 25 million/km for the costs anyway.

HSR infrastructure emissions

The first source for the emissions is a report from the UIC, the International Association of Railway Companies, from 2016. Their model, with 15% tunnels, results in 127 tons of emissions per km per year, thus 127 grams/pkm when you have a volume of one million passengers per year. However, they indicate that their data is somewhat incomplete. Not all sources of emissions could be included.

Perhaps that is why this value too appears to be a bit on the low side compared to the HS2, for which extensive data is available, in the public domain to boot. With 10% tunnels in 2011, they give 5,333 tons per km, which, if depreciated over 40 years, comes down to 133 tons/km/year. With 15% tunnels, that would be 185 tons/km/year. Here too, however, conservative calculations have been made and the emissions are assumed to be 127 tons/km/year.

Detour factor

Although the destinations are selected based on distances as the crow flies, this is of course never the route that an HSR or an aircraft actually follows. For example, the Amsterdam-London route by HSR is 50% longer than the distance as the crow flies. The average detour used is 35% for trains and 15% for aircraft. For trains, the detour is often determined by geographical circumstances, such as in this case the location of the North Sea. With aircraft, the detour is usually caused by airspace being reserved for military use, plus detours at an airport to take off and land against the wind as much as possible.


The last factor that effects the outcome of the calculations is the depreciation period. Customary is 15 years for the electrical installations, 35 years for the track itself and 60 years for tunnels. An average of 40 years has been used in the calculations, assuming 15% tunnels. With a higher percentage the average depreciation period could also increase somewhat.

Zero-emission electricity

When in the future all electricity is generated emission-free, only the infrastructure will matter. The load factor is no longer relevant because the infrastructure costs and emissions are shared by the number of passengers only. It makes little difference whether those passengers are transported on almost full or on almost empty zero-emission trains.

Calculation of this scenario shows how dominant infrastructure is. Because even then, in terms of costs per ton avoided, the aircraft will remain the better option for a very long time. The tipping point for he costs per ton avoided moves back from 30 million to 20 million passengers per year.

Using the more realistic costs of 50 million per kilometer shifts the tipping point for zero-emission electricity to 38 million passengers.

In that situation, depreciation over 60 years brings the tipping point to 25 million passengers per year. That number is expected for HS2, but none of the options proposed by Royal HaskoningDHV even come close.