Reduce Air Travel
within Europe

GEO454 Project (FS23)
Group 5

SDG 11
popular intra-European air routes
(in 27 countries)
(in 2019)
emitted tons of CO2
(in total)
% of which could well be reduced
(by the use of alternatives)

[for more details and explanation of these findings, view the results section]


Representing an immense international effort, the United Nation (UN) has established the 2030 Agenda for Sustainable Development which aims to achieve global sustainability in environmental but also social and economic terms. In particular, these ambitions center around the 17 Sustainable Development Goals (SDGs) and corresponding sub-goals which individually tackle specific issues.

Our research project aims to contribute to the achievement of SDG 11.2 which targets to "[...] provide access to safe, affordable, accessible and sustainable transport systems for all [...]". In an European context where public transport is already widely available, this translates to the need of a shift in mobility behavior. To be specific, this means that air travel should be reduced and replaced by sustainable alternatives such as trains or busses.

However, the replaceability of air travel is highly debated since alternatives appear to be percieved being rather slow, rare, unreliable, and/or expensive. This work therefore tries to fill the gap and identify the replaceability of particular air routes. This is done by visualizing the top 3 most popular intra-European air routes per country which then can be interactively selected to show facts about the available alternatives and corresponding replaceability.

We therefore seek to answer the following research questions:

(1) Which of Europe’s top 3 most popular air routes per country can and cannot be appropriately replaced by sustainable alternatives?
(2) What are potential reasons for the discovered spatial patterns in popular air routes and their replaceability?

Data & Methods

Our approach is based on the top three most popular air routes per country. The data sources from Eurostat [1] and represents the pre-covid situation in 2019. The countries included represent the European Economic Area (as well as Switzerland and the United Kingdom). However, we excluded Iceland, Malta, Cyprus and oversea territories due to their isolated location without realistic travel alternatives.

Furthermore, we statistically aggregated the data on multiple levels. (1) Passenger volumes are displayed as a total of flights in both directions (A-B and B-A volumes count to the same air route). Presented air routes are non-specific in direciton. (2) In the case of multiple airports per city, the flights were summarized to city-to-city connections (A1-B2, A2-B1, etc. all count to the same AB air route). Passenger counts represent all passengers on all possible flights between two cities. (3) The top three routes were selected per country. Certain routes might be among the most popular twice, but are only illustrated once. Nonetheless, every country features (at least) three flights.

After identifying the routes, alternatives were researched. The alternative types and connections were found via various travel planners (Omio [2], Rome2Rio [3], Rail Europe [4]). Only regular connections were consiedered; the fastest one was to be selected. The carbon emissions were assessed via different tools and statistics (Myclimate [5], Ecopassenger [6], World Land Trust [7], Statista [8]).

Lastly, the recommendability was assessed individually according to certain criteria. The first indicator is travel time: according to literature, travel times of around six hours or less are "directly competitive" to flights [9]. We therefore conclude that alternative journeys with travel times up to around eight hours are at least recommendable. A further aspect involves convenience: connections with few changes are preferable while multiple changes reduce the recommendability. The overall classification was then made based on a mix of the involved factors. Long journeys without changes (ideally via night trains) can therefore be recommendable nonetheless. The replaceability recommendation "Yes" was given for trains with less than 8h of travel times if involving few changes or for longer journeys if direct night trains exist. "Maybe" was selected if the journey can be made within one day or if convenient direct connections exist (e.g., overnight ferries, night train with one additional change).


Displayed below is an interactive map containing the identified top three routes per country and the corresponding information on alternatives which can be found when selecting one particular route. The map can be opened in a new tab seperately here.
[The website and embedded map are optimized for desktop view. In case of mobile use or similar visualization errors, open the map separately.]

Conclusion & Findings

Air Travel is (Partially) Replacable!

Air travel clearly plays an important role in European travel behavior. Interestingly, a surprisingly large fraction of routes could be replaced by trains, busses, and/or ferries. However, this comes at an increased travel time and also higher financial costs. Replaceability is especially available in western and central Europe, with eastern Europe lagging behind.

Alternative Travel Saves Emissions!

If combining the clearly and potentially recommendable alternative journeys, a total carbon reduction of up to 55% could be reached. Even though all types of travel cause certain CO2 emissions, trains, busses, and even ferries, are much less harmful than planes. Moreover, airplane emissions are more harmful due to the direct atmospheric release [10].

Mobility Remains an Issue!

However, it must be acknowledged that air travel is not the sole environmental issue. Mobility always comes at a certain environmental cost; even the alternatives cause considerable emissions. It is therefore important to understand that there are only more harmful and less harmful travel types - but no perfectly environmentally friendly one.

Main Findings:
- Our research has analyzed the top three most popular air routes per country in Europe. We found out that a substantial share of those flight routes (51 out of 79) cover ranges which could also be made by less environmentally harmful alternatives. This concerns 75.12% of all passengers on those routes. Taking these passenger volumes into account, this would translate to an overall maximum emission reduction of 55.01%.
- The replaceability of connections however varies enormously. The two determining components herein are Europe's geography and the presence of (high-speed) rail services. Air connections spanning across seas and/or mountain ranges are typically much less easily replacable than those covering rather uniform topographies. The most appropriate alternatives are usually high-speed rail services - which however are not available everywhere. Other alternatives usually appear to struggle due to significantly longer travel times.
- All of the 10 most popular flights by passenger numbers are potentially replaceable ("yes" & "maybe"). This illustrates the enormous potential of sustaineble travel alternatives. Also, our results confirm that flight duration seems to be an appropriate proxy for replaceability. Almost all flights below 2h of travel time (except for three routes) are replaceable ("yes & "maybe").

Further Elaboration:
- Interestingly, a majority of the European countries have their most popular flight going to/from London. Besides the city's economic importance, this likely indicates that many of those flights serve as connection flights. This is an important finding in terms of replaceability: it is therefore possible that there is less tolerance for rather long travel alternatives if it only replaces a section of the overall journey.
- An overall pattern is hard to define due to variations in geographical, social, and economic contexts. However, some interesting notes can be made: for instance, the Paris-London air corridor is surprisingly not a national top-three route despite the very high mobility between those places. This can be explained by the Eurostar service through the Eurotunnel which since its construction has notabely reduced the market share of air travel between those two metropoles [11]. A similar role model can be found in Spain where travel between Barcelona and Madrid is very popular. Nonetheless, this air route is not among the country's most popular. This is due to the extensive high-speed train capacities on that route which has already shifted mobility behavior two decades ago [12].
- Meanwhile, the popularity of certain routes indicates the deficits that alternative travel modes have. For instance, the Oslo-Bergen air corridor experiences particularly high demand and covers an unusually large travel market share. This is mainly due to the geography and consequent lack of alternatives. Even though rail lines exist and work properly, they are already operating close to their limits. There is simply no existing capacity favor a further shift from air to rail travel [13].
- This highlights the importance of sufficient transportation infrastructure. The entire scenario of shifting away from air travel is only possible if adequate infrastructure is available. If a substantial shift in mobility behavior should sustain and even further improve, it is essential that on-land travel capacities can be expanded accordingly. This is currently not the case everywhere which undepins the challenges of sustainable mobility. That is however very problematic due to the complpexities involved in rail infrastructure expansion [14].

Answering the research questions, our work allows for concluding the following:
(1) Air travel's prominence is high. Out of Europe's top three most popular air routes per country, only 28 out of 79 are not replacable by environmentally friendly alternatives. As this theoretically concerns 75.12% of all passengers and would reduce 55.01% of the emitted CO2 emissions.
(2) The spatial patterns discovered highlight the importance of London (but also other larger/central western European cities) as an European travel hub. Therefore, the replaceability of popular flights is to some degree depending on the proximity to central/western Europe. Geography thus plays an important role. The most-suited routes for replacability lie mainly - but not exclusively - within central and western Europe where high-speed rail services are available. Irreplaceable routes are mainly covering on-ground impassable topographic hurdles such as seas and extensive mountain ranges.
(+) Furthermore, not all theoretically replaceable flight routes could be really really replaced. This is due to capacity limitations which must be overcome in the near future. Additionally, one must accept that all forms of mobility are somehow harmful to the environment. The minimum goal should therefore be to limit the most harmful ones to an absolute minimum while simultaneously reducing mobility as a whole.


Conceptual Issues:
Besides these interesting results, conceptual limitations must be acknowledged as well. Most importantly, our approach only searches for the fastest alternative and does not show the broad variety of alternatives. Second, routes with connecitons allow for the risk of missing the following leg during a layover - which is not accounted for in this work. Furthermore, the financial aspect was only covered partially due to the limited scope of our project. Similarly, the classification of replaceability is not perfectly uniform and general. Moreover, the question remains whether the available alternative capacities would be able to carry substantial numbers of former flight passengers. The scenario is therefore only theoretical and not yet practically implementable at a full scale. Nonetheless, it might serve as a starting point for the further development of sustainable transport and ignite at least a minor shift in mobility behavior. We advise that a more detailed small-scale spatial analysis of train travel times should be included, for isntance by including platforms such as "Chronotrains" [15].

Technological Issues:
When working on the visualization, certain technological limitations affected our resulting map as well, especially due to working with an ESRI Dashboard. On the positive side, the dashboard enables easy visualization of spatial information and has a user-friendly design. However, making custom changes to the dashboard beyond standard functions can be challenging and may require advanced programming skills. This includes some basic functions that would have contributed towards improving the functionality for our dashboard.
For instance, it was difficult to define the standard map extent (we solved it via a trial-and-error approach). Using the predefined option of selecting a fixed scale did not help in our project. Moreover, the result highly depends on the display size - the map will therefore look different on different displays. This is especially tragic for in-map elements (e.g., text boxes or filters). This is unfortunate since ESRI Web Apps are testable at different display layouts while dashboards are not. Similarly, the dashboard does not allow for positioning the pop-ups at a certain location.
However, the biggest problem that has significantly limited the functionality of our dashboard is the linking of the different dashboard elements effectively. Clicking on flight routes within the main map, for example, does not dynamically update the information displayed on the right-hand side of the dashboard. It is only possible to configure the widgets so that they match the elements visible on the map. As a workaround, a "Select a specific flight" selector was introduced to display individual flights on the map and link them to the relevant information.

Literature and Data Sources

About Us

Jens Grafström (e-mail)
Concept Design, Web Design
Aleksei Ilchenko (e-mail)
Data Acquisition, ArcGIS Operation
Rainer Gardeweg (e-mail)
Data Processing, ArcGIS Implementation