Urban Digital Twins for Smart Cities and Citizens:The Case Study of Herrenberg, Germany

Cities are complex systems connected to economic, ecological, and demographic conditions and change. They are also characterized by diverging perceptions and interests of citizens and stakeholders. Thus, in the arena of urban planning, we are in need of approaches that are able to cope not only with urban complexity but also allow for participatory and collaborative processes to empower citizens. This to create democratic cities. Connected to the field of smart cities and citizens, we present in this paper, the prototype of an urban digital twin for the 30,000-people town of Herrenberg in Germany. Urban digital twins are sophisticated data models allowing for collaborative processes. The herein presented prototype comprises (1) a 3D model of the built environment, (2) a street network model using the theory and method of space syntax, (3) an urban mobility simulation, (4) a wind flow simulation, and (5) a number of empirical quantitative and qualitative data using volunteered geographic information (VGI). In addition, the urban digital twin was implemented in a visualization platform for virtual reality and was presented to the general public during diverse public participatory processes, as well as in the framework of the "Morgenstadt Werkstatt" (Tomorrow's Cities Workshop). The results of a survey indicated that this method and technology could significantly aid in participatory and collaborative processes. Further understanding of how urban digital twins support urban planners, urban designers, and the general public as a collaboration and communication tool and for decision support allows us to be more intentional when creating smart cities and sustainable cities with the help of digital twins. We conclude the paper with a discussion of the presented results and further research directions

Virtual Reality Simulators for Inclusion and Participation: Broadening Perspectives on Accessible Cities and Public Space

The design of urban public space often involves a convergence of different actors with different priorities in the use of available space. This becomes evident when different modes of transport are combined in the very limited space available. At the same time, the growing and aging population strengthens demands for action in public space design towards better accessibility and involvement of the vulnerable. Innovations in digital design and simulation tools have shown a great demand to address these challenges as they have the potential to facilitate mediation and improve citizen science, participative and collaborative planning processes. Joint evaluation is supported and planners, decision makers and foremost citizens are brought together [(Yang et al. 2019), (Sanchez-Sepulveda et al. 2019), (Buffel et al. 2012)]. In our research, we have implemented human-computer interfaces for urban digital twins. These digital twins combine geometry and point cloud models, simulation results, and sensor data and enable analysis of existing situations, scenario testing, as well as prediction, on all urban scales, from buildings to cities and regions. By visualization in VR environments such as a CAVE (Cave Automatic Virtual Environment) they provide a powerful method for informed discussions between all stakeholders which is essential for joint decision-making. Our recent work extends these tools to include often neglected groups, such as people with disabilities, the elderly, or children, with the aim to empower them and to address their specific needs with respect to public spaces, while making these needs more traceable for others. Therefore, we have implemented different modes of traffic in simulators: Cars, bicycles, skateboards, and wheelchairs. Using one of these simulators, users can then interactively explore virtual replicas of public spaces using a real vehicle for steering. In combination with a tracking system, the user’s perspective in the virtual world is adjusted accordingly, enabling an impression of riding through the replica similar as in a real environment. Users can explore the accessibility of public spaces and detect shortcomings like high curbs or slopes. Often, these are unnoticed by pedestrians while posing major obstacles for people in wheelchairs, with strollers or roller walkers. Hence, this simulator helps to better understand and include the mentioned group in public participation. Moreover, the simulator was combined with traffic simulations (Zeile et al. 2021). These, in particular when visualized along with the digital twin, improve the depiction of the actual processes and dynamic scenarios, and allow to simulate and compare scenarios of different design proposals. Bottlenecks such as narrow sidewalks incapable of handling the load of pedestrians, or unclear intersections with an insufficient view can be detected as well as the use of space in certain conditions as during rush hours or at construction sites. Experiments were carried out using the different simulators as human-computer interfaces. Observations and questionnaires were used to analyse the experiences of 23 test subjects. In summary, the developed simulators are intended to contribute to safer and better accessible urban spaces for all. In this initial work, the focus lies on groups with special needs in public spaces - for example, highly mobile young people and in contrast people with limited mobility or the elderly. By detecting current barriers, the developed simulators make them tangible and understandable for the wider public but also for planners, designers, and decision-makers