Prof. Kay Axhausen is a researcher at the Institute for Transport Planning and Systems at ETH Zurich. After completing his studies and doctorate in Civil Engineering, he worked at several international universities before being appointed to ETH Zurich in 1999. His field of research includes mobility behavior, traffic modeling and traffic planning, with a particular focus on the empirical analysis of mobility data and the modeling of decision-making processes in traffic. Prof. Axhausen is one of the leading figures in modern transport research. His scientific work has received numerous awards and is recognized worldwide in the professional community.

During his stay at the Faculty of Transport and Traffic Sciences, Prof. Axhausen gave a guest lecture on the topic of "E-Bike City". This week he will also take part in a workshop on "Mobility and Time Use" as part of the research activities of the Collaborative Research Center "AgiMo: Data-driven agile planning for responsible mobility".

We spoke to him about his field of research and current developments in mobility research.

LD: Welcome to the Faculty of Transport and Traffic Sciences, Prof. Axhausen. You research in the field of transport planning. First of all, what originally brought you to transport science and what fascinates you about your field to this day?

KA: My original interest was in urban planning. Urban planning naturally leads to cooperation and overlapping with traffic, so I ended up with traffic behavior and stayed there. But then I always understood traffic behavior as part of spatial behavior and also looked at urban planning or real estate aspects in this context.

LD: In your opinion, what has changed in transport research in recent years and where do you see particular potential for development?

KA: When I look back, transport research has changed fundamentally over the last few decades. When I started out, data sets such as the former KONTIV - today's Mobilität in Deutschland (MiD) - were the largest surveys available in the German-speaking world. From today's perspective, these data sets are tiny compared to what we can collect and analyze today. The transition from comparatively small, standardized surveys to extensive big data sources is one of the key upheavals of recent years.

A second major change concerns the methods. At the beginning of my career, discrete choice models were still considered almost revolutionary in German-speaking countries. Today, they are firmly established and are increasingly being supplemented by machine learning approaches - not replaced, but usefully expanded. This results in new research fronts and questions.

Finally, the social context has also changed considerably. When I started in transportation research around 40 years ago, climate change hardly played a role. Today, it is at the center of almost all debates. Accordingly, the focus is shifting to the question of what effects transport policy measures actually have and how they can - or should - contribute to overcoming this global challenge.

LD: What role do new data sources and new tools such as big data and artificial intelligence play in current research?

KA: Machine learning approaches basically offer a way of dealing with the growing flood of data and making large amounts of data accessible in the first place. The term "machine learning" is now used very broadly - sometimes so broadly that even classic regression models are subsumed under it. It is important to take a close look at which methods are actually being used and what the underlying interest in knowledge is.

Essentially, the aim is to make large, often continuous volumes of data analyzable and to better understand their dynamics. A particular strength of machine learning methods lies in their ability to map complex and non-linear relationships and capture interactions that traditional approaches can only deal with to a limited extent.

LD: What contribution can transport research make to making mobility more sustainable and socially just?

KA: The question of how transport research can contribute to sustainable and socially equitable mobility has been with us for a long time - and is also frustrating to a certain extent. After all, many solutions are already known. As early as the 1920s, Arthur Pigou showed how traffic volumes could be controlled by means of prices. So we know what would be effective in theory, but at the same time we can see how difficult it is to implement such measures politically.

We therefore inevitably have to look at alternatives that are politically feasible. The framework conditions vary greatly from country to country. In Singapore, the political assertiveness of the government made it possible to introduce road pricing at an early stage. In London, on the other hand, this was only possible after the city government was once again given the relevant powers - in fact, the introduction of road pricing was one of the few traffic policy levers that the Mayor actually had at his disposal.

In Switzerland, on the other hand, the Federal Roads Office has tried several times to introduce mobility pricing into the political debate - both attempts were thwarted. That shows: We know what we could do, but are coming up against political limits. This raises the question of what other avenues are open to us.

One approach lies in technical development, such as reducing CO₂ emissions directly at source. But it is questionable whether this alone will be enough. In Zurich, we have therefore recently been working on an alternative concept, the so-called E-Bike City, which I will also be talking about in my presentation. This approach addresses the issue of sustainability, but at the same time deals with questions of social justice in a different way.

Price or quantity-based control instruments always raise the question of who can afford mobility and who cannot. This quickly leads us into distribution debates that are often dominated by individual cases instead of looking at the effect on society as a whole. The idea of the E-Bike City poses these questions differently: it focuses on a structural transformation of the city that affects everyone.

The central question is no longer primarily one of money, but of participation: Which people are excluded due to physical limitations, and how can this be dealt with? This is a challenging but fundamentally different discussion to the one about prices and ability to pay - and, in my view, one that opens up new perspectives for socially just and sustainable mobility.

LD: What constitutes socially just mobility?

KA: Social justice is a much broader concept than just participation in transportation, and that's what makes it complex. Basically, social justice is first and foremost a moral and political concept: it is about the question of what society wants to enable every member to participate in, at least as a minimum. This immediately raises questions such as: Who defines this "minimum"? And who belongs to society at all? Some say only people who have lived here for decades, others take a more inclusive view - this is also part of the political debate.

Transport science alone cannot answer these questions; we are neither moral philosophers nor political scientists. Our contribution is to focus the discussion on our field of research: What effects do different framework conditions have on participation in social life, mediated through mobility?

Today, this view is also being broadened by digital possibilities: We can increasingly analyze how mobility and social participation can also be mapped and supported electronically. In this way, our scientific contribution can be meaningfully integrated into the wider social debate.

LD: In your view, how can the bridge between scientific research and transport policy decisions be successfully built?

KA: Bridging the gap between scientific research and transport policy decisions is a complex issue and depends heavily on the political context of a country. First of all, it is important that there is a certain consensus within the discipline. Only if an idea is recognized as robust by the professional community can it be credibly introduced into the political debate - otherwise you run the risk of being dismissed from the outset.

Let's take Switzerland as an example: two years ago, there was a referendum on the construction of six highway projects. In the public debate, there were two opposing groups: the supporters, who emphasized short-term congestion relief above all, and the critics, who included many experts. The latter pointed out that the expansion would only have an effect for a few years before the known induced traffic would eat up the benefits again. Ultimately, the federal administration lost the referendum and was faced with the challenge of reallocating the funds. Peers were able to exert influence by publishing a joint open letter, which was signed by numerous experts - a direct and public intervention in the political process.

In Germany, the influence on political decisions is different. There are no referendums of this kind here. Involvement is more indirect, for example through participation in preparatory planning processes such as federal transport route planning. For example, Professor Nagel (TU Berlin) and I were involved in the last planning process by determining the value of time. Together with a survey company, we carried out a large-scale study, the results of which were then incorporated into the models and thus influenced decisions.

So you can see two different mechanisms: on the one hand, a direct influence through participation in public debates and decisions, and on the other hand, an indirect influence through methodological contributions that improve the basis for decision-making. Both paths are necessary and complement each other.

LD: Let's move on to teaching and knowledge transfer. What would you like to pass on to transport science students?

KA: First of all, I would like to give students a solid technical and methodological education. It is important that they understand the consensus of the subject, but at the same time also know the different points of view. Students should be encouraged to form their own opinions, think critically and develop their own positions.

Our aim is not to provide ready-made opinions, but to enable young professionals to approach the issues of transportation science well prepared and to master the methods in order to be able to make their own reflected decisions.

LD: Are there any changes in the demands placed on students today that may have been different a few years ago? Are there skills that might be needed more today and in the future?

KA: Changes in the requirements for students depend very much on the area of transportation science in which they want to work. The subject is very broadly based: Some students are interested in railroad systems or the operation of transport systems, others in transport and business administration or large-scale forecasting models in transport planning.

There is also the later role in professional life: Will you be working "behind the scenes" on models, or will you be in direct contact with customers and the public on a daily basis as a manager of a transportation company? The skills required vary considerably depending on the profile.

Our task is to prepare students for the current state of knowledge and technology, to familiarize them with the methods and to enable them to critically question and further develop them. This enables them to make informed decisions and actively contribute to the further development of the subject, regardless of the field in which they later work.

LD: Finally, two personal questions. Firstly, what are you currently reading?

KA: At the moment I'm reading "Wie konnte das geschehen?" by Götz Aly and "Alles, was wir nicht erinnern" by Christiane Hoffmann.

LD: And finally: How do you look back on your time here at our faculty and what plans do you have?

For me, the next few days will be all about getting to know each other. I would like to get to know my colleagues here at the Faculty better and also get an idea of Dresden - I have only seen the city briefly so far.

LD: We hope you enjoy your visit. Great to have you here and thank you very much for the interview.