Digital twins: Duplicate city

It's Tuesday afternoon between 4 and 6 p.m. in Nuremberg. People have finished work and are starting their journeys home through the northern Bavarian city, which is home to around 550,000 citizens. The result: traffic jams. The A73 city freeway is blocked, and crowds are packing into the subway. It's a situation that repeats itself just about every afternoon. However, this could change in the future... if Nuremberg manages to duplicate itself. Only in virtual terms, of course – by creating a digital twin of the city! This digital representation would show traffic flows, buildings, green areas and much more. There's enormous potential in the simultaneous recording and mapping of movements of people, vehicles and goods: If you record such data across an entire city, you can understand, simulate and steer the corresponding flows. This might reveal how great an obstacle a particular construction site actually is, for instance. And traffic is just one aspect of the potential: Registering photovoltaic systems makes it possible to steer the urban energy transition, and usage data enables the selective planning of entire districts.

Every subway passenger is a data donor

For this purpose, the city of Nuremberg took part in the EU-funded “twi.N City” project, which aims to develop a city model based on geodata. The hope is that it will be possible to use the data to draw conclusions about visits to downtown Nuremberg and how attractive the area is. The city's transport operator, VAG, was also involved. The subway in Nuremberg has long been relying on extensive data collection and use, particularly since a driverless, fully automated subway system was put into operation in 2008 – long before the term “digital twin” was used in reference to cities. “Integration is everywhere,” says Andreas May, who was involved as a project leader in the implementation of the driverless subway and is now the head of rail operations at VAG. For him, purely driving-related operations are also just part of the potential to use the data at hand. Every passenger in the subway is a data donor. During their journeys through the city, people generate movement data that provides details about the traffic flows in the entire city.

In the twi.N City project, the VAG data was supplemented with information about parking garage occupancy and the weather. This has created a comprehensive picture of the current activity in the city. That includes Adlerstraße in the city center, which is a street that runs between two counting points installed at subway stations. A dashboard shows that an average of 39,797 people pass through the area around Adlerstraße every day, and they typically spend a considerable amount of time there. At the same time, the occupancy of the nearby parking garages indicates how many people travel to the city center by car. Adlerstraße is a pilot project for showing how data can be recorded and collated in order to derive subsequent measures to make the area more attractive.

Nuremberg is just one of several cities that have taken on the challenge of creating an urban digital twin. At present, there are several initiatives underway across Germany; the funding project TwinBy, for example, is planning to produce 18 urban digital twins in Bavaria alone by March 2024. The concept of digital twins actually emerged quite a few years ago thanks to the growing possibilities afforded by digitalization and data collection. A digital twin is intended to be a representation of a structure that exists in the physical world. This makes it possible to run simulations of various adjustments, and it also reveals dependencies between various organizations at a glance.

Avoiding redundant data storage whenever possible

In this process, there are all sorts of obstacles to overcome because, in the past, data in cities was often stored in insular solutions. Utility companies rarely collaborated with urban planning departments, for instance. One major challenge is the lack of the necessary interfaces. This is why the Bavarian State Ministry for Digital Affairs has worked with the Technical University of Munich within the TwinBy project to produce a guide that municipalities can use as orientation. The document's 80-plus pages describe the process using the concept of Smart Data District Infrastructure (SDDI). The aim of SDDI is to link platforms together using open, standardized interfaces. This is meant to improve interoperability between the various stakeholders and prevent any redundant data storage. After all, creating a digital twin is a difficult undertaking that needs support. Municipalities therefore often work together with external service providers from the field of data collection. The digital twin acts as a foundation for a cross-sector data structure and as an application-oriented link that connects existing models, data, sensors and their use in complex planning scenarios.

Benefits for smaller towns, too

It's not just major cities that can benefit from guidelines such as the one provided by TwinBy. This past spring, a digital twin was also presented in Forchheim, a district town with 34,000 inhabitants about 30 kilometers north of Nuremberg. Its twin is now freely accessible to its citizens. The town worked with RIWA GmbH, a service provider that deals in digital geodata collection. The digital twin now shows users its tree register, parking lots, playgrounds, vacant buildings and more. Even approved construction plans are stored in it. “We've been tasked with creating an organized data infrastructure that also incorporates all the relevant authorities,” explains Matthias Hoffmann, who is responsible for Forchheim's digital twin. Like Nuremberg, Forchheim faced the challenge of having several different data silos that didn't allow for any interchange. The digital twin now provides exactly that: All sorts of authorities – from the parks and gardens department to municipal management – can access the platform and exchange their data.

For Matthias Hoffman, it also offers the right kind of opportunity to engage in dialog with citizens. “The digitalization involved ensures transparency,” he explains. In the future, the plan is for the people of Forchheim to benefit even more from the data; for instance, Hoffmann and the town's administration would like to provide a digital option for building permit applications. He sees even more potential, as well, including in the possibility to monitor carbon dioxide levels through the information stored in the tree register. The town planning department would then be able to design urban spaces more sustainably and thereby boost quality of life. Hoffmann also believes there's a clear trend towards communication among various digital twins. “They're going to be interconnected," he states with confidence.

Exchanging data in Leipzig, Hamburg and Munich

The idea that the digital twins of various towns and cities could be interlinked isn't just a pipe dream. In fact, Hamburg, Munich and Leipzig are already working together in the research project “Connected Urban Twins”. “We think there's a huge opportunity in intermunicipal cooperation,” explains Mirko Mühlpfort, project leader for Connected Urban Twins in the Digital City department in Leipzig. In particular, he sees a major advantage of digital twins in the field of sustainable city development. A city's digital copy can map its solar potential, which simplifies both heating and energy planning. If cities keep getting hotter in the future due to climate change, their digital twins can be used to plan fresh air corridors. Along with energy-related issues, life in the city is being addressed as a whole. In infrastructure planning, for instance, it's possible to ascertain immediately exactly how reachable child daycare centers are for families. The results can then be incorporated into the planning of the respective city's daycare network, which can ultimately make it easier to balance work and family commitments.

The CUT project's main task lies in merging existing solutions together. “Essentially, the technical solutions have already been developed,” Mirko Mühlpfort points out. Bundling these digital products is now the task of every project team involved in creating digital twins, he continues. At present, it is indeed fair to say that not everyone is immediately on board when the idea of producing a digital twin comes up. “We often need to do a lot of convincing,” Mühlpfort admits. After all, the idea of sharing their own data tends to be a deterrent for companies at first. Mühlpfort believes the effort is worthwhile because in the end, it leads to cities with a higher quality of life, optimized architecture and less traffic. The data collected also has to be secure, of course – any potential for abuse must be minimized. This security can also have an influence on the acceptance of digital twins. In Nuremberg, for instance, the digital infrastructure of the subway has been completely segregated from other nearby networks that would be accessible via WiFi. At the same time, the population has to be involved in the process. If passenger flows are recorded in subway stations, the purpose needs to be clear. “We're not aware of any concerns in the general public about our collecting the data,” stated the Nuremberg city administration in the twi.N City project, adding that no personal data was involved.

Getting the population on board

The notion that the process of building a city's digital twin has to involve the people who live there is also the subject of research at the City Science Lab at HafenCity University (HCU) Hamburg, which is also taking part in the CUT project. One of the lab's academics, Till Degkwitz, argues that there needs to be a constant focus on the utility digital twins are meant to offer. “They aren't an end in themselves,” he asserts. It's therefore important to remember the areas in which digital twins can bring their real strengths to bear. Hamburg, for example, concentrates a great deal on social aspects and citizen participation. After all, data on people in cities is crucial for digital twins. “A city's official data only reveals part of the wider reality,” Degkwitz explains. As an example, he points out how data related to unpaid care work in civil society offers numerous insights into how people live together in a particular place. Digital twins are also helping Hamburg plan child daycare centers, schools, and green spaces in locations that maximize their social benefits.

Artificial intelligence already a consideration

Till Degkwitz can foresee AI technologies being an integral part of digital twins in the future. This would facilitate an entire network of intelligent traffic lights that could react in real time to the current traffic situation, for instance. However, Degkwitz warns against getting carried away by the promise of such ideas. “I think it's going to take a long time for us to reach that point,” he says. Even so: Digital twins are already showing their strengths, and working without them will become inconceivable in the future. “They’re simply fantastic support tools,” Degkwitz affirms. Project leader Mirko Mühlpfort agrees: “In the future, integrated city development will no longer be possible without digital twins.”

Julian Hörndlein is a freelance technology journalist in Nuremberg.