From the drawing board to digital infrastructure: Karl Nachtigall looks back on over 30 years of transportation research

The Faculty is bidding farewell to Prof. Dr. Karl Nachtigall, holder of the Chair of Traffic Flow Science, on his retirement. On the occasion of his upcoming retirement, the professor has invited to a farewell lecture today. We took a look back with him at his time at the faculty and talked about his plans for the future.

Prof. Nachtigall's academic career began at the University of Hanover, where, after studying mathematics, he completed his doctorate on linear mappings in lattice spaces in 1989. In 1999, he habilitated at the University of Hildesheim on the topic of periodic network optimization and cycle timetables. After working as a Research Associate at the University of Hildesheim, his professional career took him to the German Aerospace Center (DLR) before he took over the Chair of Traffic Flow Science at the "Friedrich List" Faculty of Transport and Traffic Sciences at the TUD Dresden University of Technology in 2000.

© TUD | Andrea Surma

As holder of the Chair of Traffic Flow Science, Prof. Nachtigall's research and teaching is dedicated to Operations Research with a focus on mathematical modelling and algorithmic optimization of rail and air traffic systems. His core research areas are in particular the construction and allocation of timetable routes, the generation of route networks and interval timetables, vehicle scheduling and air traffic flow control. In terms of methodology, he combines system analysis, mathematical and data-based modeling with the development of practical software solutions. Numerous third-party funded projects and international publications demonstrate the transfer of his research into real applications in rail and air traffic.

LD: Prof. Nachtigall, when you look back on your scientific career: How has traffic flow theory changed since your beginnings and what has always particularly fascinated you about this field?

KN: I definitely see the biggest changes in digitalization and the potential it offers. One example: shortly after the fall of the Berlin Wall, around 1990, I started as a mathematician at Deutsche Bahn and worked on timetable design. Back then, visual timetables were still drawn on large drawing boards with a ruler. Today, you can depict almost the entire infrastructure of Germany on a laptop - every signal, every turnout, countless timetable variants. This development is still fascinating for me. The dimensions have changed enormously and digital processes are now an integral part of many transport companies.

LD: Which of your research projects would you describe today as particularly formative for your own work and perhaps also for the field as a whole?

KN: A key milestone was the digitalization and optimization of timetables. Together with Deutsche Bahn, we developed corresponding models over many years - supported by numerous dissertations and doctoral theses. This ultimately resulted in a productive application: the so-called click-and-ride app. Today, freight train paths can be booked in just a few minutes. It is very pleasing to see that many of the originally developed models are now being used in practice, even if individual details have been adapted over time.

LD: Traffic flow models are often highly complex. To what extent do theoretical findings from traffic flow theory actually find their way into traffic planning and political decisions and where has their potential remained untapped to date?

KN: There are certainly successful examples. In addition to the railroads, for example, we have developed models for route network planning that have been tested by Leipzig's public transport operators. Although the results were not adopted one-to-one, individual approaches were incorporated into new network concepts.

Another project concerned optimizing the use of runway capacities in air traffic control. The system was technically mature, but was not implemented for political and economic reasons. Ultimately, many external factors play a role here - sometimes the transfer is successful, sometimes not. Political decisions can only be influenced indirectly, for example by specialist personnel who can communicate the models convincingly.

LD: Transport is increasingly caught between the poles of digitalization, automation and climate protection. Which of these developments do you think will have the most lasting impact on the flow of traffic?

© TUD | Andrea Surma

KN: In the short term, digitalization and automation will have the greatest impact. Nevertheless, I would like to see climate protection come back into focus. Significant contributions can be made by bundling public transport. In combination with resource efficiency, such models could have an even greater impact in the future. Technically, thanks to enormous computing power, we are now able to solve problems that were unthinkable 30 years ago.

LD: You have educated students for many years: What skills or attitudes do you consider essential for early-career researchers today?

KN: It is crucial that students understand the structures behind the models and do not rely solely on software or automatic outputs. Figures need to be critically scrutinized. That's why I still think it's important to develop content in the traditional way on the blackboard and to make connections visible. University education should not only impart up-to-date knowledge, but also promote fundamental understanding, because methods and technologies are constantly changing.

LD: Let's look ahead: what open questions in traffic flow theory would you like to see answered by the next generation?

KN: Many challenges are related to the high complexity of the problem. Some tasks belong to the so-called NP-complete problems, whose computational effort is growing exponentially. Even modern computers are reaching their limits here. Progress in this area would be highly desirable, as the practical need is great.

LD: If you could give your younger self a single piece of advice as a scientist, what would it be?

KN: I would recommend not to focus exclusively on big data and artificial intelligence. These methods are valuable, but not suitable for all issues. Traditional algorithms, models and structured approaches remain important. A balanced combination of both worlds is crucial in both research and teaching.

LD: What plans and intentions do you have for your retirement?

KN: I will continue to supervise two doctoral students, including on optimization issues at Deutsche Bahn, such as the organization of test runs for rail infrastructure. I am also planning further projects with Deutsche Bahn and Leipzig's public transport companies. I also volunteer as a hospice companion. This work forms a deliberate contrast to the technical and scientific world and I personally find it very enriching. Privately, I am also planning a longer trip around the world lasting around two and a half months, which I would like to use to ring in my retirement.

LD: We would like to wish you much pleasure in doing so. Thank you very much for your time and all the best for you.

KN: Thank you very much. I look back on my time here with great gratitude. I have always enjoyed working with colleagues and students. I wish the Faculty continued success on its path.

Acknowledgements

The Faculty of Transport and Traffic Sciences would like to thank Prof. Karl Nachtigall for his many years of commitment to research, teaching and academic self-administration. With his great professional expertise, he has significantly shaped the development of transportation flow theory and accompanied numerous students on their academic and professional path. Particularly noteworthy is his lasting contribution to the transfer of scientific knowledge into practice as well as his always open, collegial and supportive attitude towards early-career researchers. The Faculty wishes Prof. Karl Nachtigall good health, happiness and many more inspiring projects in the new phase of his life.

Background: Traffic Flow Theory at the "Friedrich List" Faculty of Transport and Traffic Sciences

Traffic flow theory at the Faculty of Transport and Traffic Sciences dates back to the mid-1950s, when Gerhart Potthoff published the first fundamental work on traffic flow processes. These scientific achievements contributed significantly to the Hochschule für Verkehrswesen gaining international recognition.

In the future, the Faculty of Transport and Traffic Sciences will no longer have just a single Chair dedicated to the topic of traffic flow. Rather, the continued importance of this discipline is reflected in the current cross-structural thematic anchoring of Traffic Flow Science, for example in the Chair of Traffic Process Automation, the Chair of Transport Modelling and Simulation and the Chair of Applied Statistics. As a theoretical foundation, Transport Flow Theory offers a wide range of applications in modern transport research and is symbolic of the holistic and systemic view of mobility to which the "Friedrich List" Faculty of Transport and Traffic Sciences is committed.