Virtual Cities in Urban Planning: The Uppsala Case Study

Gearing cities towards a path of sustainability is a daunting task. The urban models that we have come to accept during the 20th century need to be revisited, but change, even if welcomed in abstract, is usually met in reality with enormous resistance from the economic and political models that underlie our cities. Some of the most powerful tools for promoting change are those related to conceptualization and visualization. When considering urban plans that aren't just incremental improvements over what already exists, city officials, urban planners and the general public must be able to visualize not just the merits of those plans in isolation, but how they interact with all the infrastructure that already exists. This paper describes one such urban plan that has been under consideration in the city of Uppsala, Sweden, for the past 5 years: a solar-powered Personal Rapid Transit (PRT) system connecting the main train station to the Hospital and the University. The process of discussing the PRT system included the development of a virtual reality simulation of parts of the city. We report on the process and role of this virtual reality simulation.


Introduction
Urban planners, real-estate developers, and the general public are aware that the current carbon based energy life is not sustainable, and that innovative approaches to urban development are needed. However, the transition into new forms of planning is quite difficult. The experience, knowledge, and execution of planning for urban developments are upheld by a fragmented base of stakeholders, many times having inconsistencies between their databases. There is no common picture of what pieces of infrastructure the cities contain, and how they operate and integrate with each other. Stakeholders' sharing data and engaging in dialog over longitudinal projects is one of the main obstacles on the path towards smart cities.
Most software tools for making 3D models, simulations, and presentations are developed and marketed assuming the above context. This means that the tools themselves are perpetuating the current fragmented structure of urban planning, becoming a limiting factor in the goal of having a holistic, contextual view of any given urban sector. The market of IT for urban planning is dominated by tools that have been focusing on specific areas of technical expertise rather than trying to support the coordination and integration aspects of these projects.
To a large extent, the popularity of Google Earth shows the need for a common information infrastructure that goes beyond what the professional desktop-based tools provide. However, as popular as Google Earth has become, the control and interaction models underlying Google Earth are lacking some important features for supporting an effective, actionable common operating picture for real urban plans. There is a void in tools and systems that target coordination and integration, that focus on context as much as content. Bettering urban planning tools by making them more holistic and collaborative, and by engaging stakeholders in the decision processes, may have an immediate impact on bettering the urban plans themselves in terms of how cities use the available resources. This general belief is shared among many researchers in urban planning (e.g. [19], [29], [32]).
3D visualization tools have long been used in architecture, real estate development and urban planning. Typically these tools have three kinds of usages: (1) marketing and community education; (2) geographic information analysis; and (3) design and engineering of buildings and structures. Marketing and community education tools consist of 3D computer animation movies usually designed to evangelize the community about the project, i.e. to sell the vision or idea; geographic information analysis tools consist of Geographic Information Systems (GIS) such as the ESRI toolset, and they are used to study the technical feasibility of the different aspects of the projects; finally, design and engineering tools include professional CAD tools such as AutoDesk that are used long after the main urban planning decisions have been made. There seems to be a gap between tools for evangelization (1) and tools for technical design (2 and 3). Yet, if cities are to engage in sustainable development, it is critical to provide tool support for frank discussion of urban planning ideas.
We posit that such gap will be filled by tools that virtualize cities, as many aspects as possible, in intuitive and accessible manners. This idea is not new. Virtual reality has been reportedly used for GIS and urban planning since the 90s (see Section 2), but somehow it hasn't quite entered the practice of urban planning, especially in early phases. Intrigued by this gap, we set to conduct a study on the use of immersive virtual reality for early stage urban planning. What are the hurdles? Who builds the models and who uses them? How do stakeholders interact with, and through, the model? Does virtual reality enable new kinds of processes and new levels of engagement, or are the VR tools just better visuals for the exact same old processes? And, most importantly, do virtual cities ultimately lead to better, more sustainable real-world city planning or are they a distraction? This paper describes the virtualization of the city of Uppsala, Sweden, in the context of a novel urban transportation system that is being considered. Specifically, city officials and several city stakeholders are considering the deployment of a Personal Rapid Transit (PRT) system connecting the main train station to the Hospital and the University. PRT, also known, as pod cars, are automated vehicles that carry a small number of passengers (up to 6) traveling together to the same destination [16]. The pod cars run on dedicated guideways, or tracks, built above the ground. Depending on the model, they can be suspended on or supported by the guideways. The most high-profile pod car system in use today is the one in the Heathrow airport, London, deployed in 2011 (see Figure 1). Another high-profile case is the PRT system currently being implemented in Masdar City [28], [30], a city designed from scratch to be energy efficient. At the core a possible PRT system in Uppsala is the belief that it would reduce air pollution, energy consumption and operating costs, while moving more people faster than cars and buses do. Over the years, proponents of PRT systems have produced several technical studies and simulations that seem to support those claims (e.g. [12], [21], [26], [27], [39]).
In spite of these concerns, there seems to be a growing interest in PRT systems because of their potential to reduce operating costs and pollution. The highly visible deployment in Heathrow may be a turning point in the public acceptance of this form of transportation. Feasibility studies have been done for a few cities in Sweden, including Uppsala [35]. Nevertheless, when officials of traditional cities and local stakeholders consider something as radical as a pod car system in their own cities, such as the case of Uppsala, technical doubts, aesthetic insecurities and a general fear of radical change are unavoidable. In [34], Tégner et al. summarize the obstacles for the uptake of PRT in Sweden.
In order to address these issues, Uppsala city officials commissioned a small 3D virtual reality study of the area around the main train station. The study was later expanded to a 3x1.5 km 2 area. These officials wanted something beyond a generic 3D computer animation movie about pod car systems --those had been done before. They wanted a virtual environment that depicted an accurate and realistic rendition of Uppsala, and that could serve as an editor for laying down the possible deployments of the track and stations, as they weren't sure what the best placements would be in the holistic context of the existing urban elements. Furthermore, they wanted a dynamic environment consisting of moving traffic and pedestrians, one that could be observed from many points of view, and that could be easily changed. In short, they wanted to have an integrated virtual rendition of as many aspects of the city as possible, so to assess the pod car system in the context of all those aspects. This paper describes the technology that was employed for meeting these requirements, and the main observations and lessons learned from this project so far, in particular the role that the virtual reality model of Uppsala played in stakeholder discussions and in the evolution of this urban planning process. Videos from this project can be found on Youtube (Site 1). At the time of writing this paper, the decision of whether to apply for funding for the PRT system is still under deliberation in Uppsala.

Related Work
Several studies exist on the use of Information and Communication Technologies (ICTs) in urban planning and smart cities, such as broadband deployment, e-services and open data (e.g. [1], [2], [6], [14], [20], [22], [23]). Those are related to this work in trying to unveil the actual experiences and observations from the deployment of technology. Our work focuses on one particular kind of technology: virtual reality.
The idea of using virtual reality for GIS and urban planning is quite old; a substantial amount of work can be found in the literature since the 1990s, when advancements in computer graphics made that idea possible (e.g. [5], [9], [15], [18], [33]). As early as 1999, researchers envisioned participatory GIS systems based on virtual reality (e.g [17], [31]). Adoption of those ideas in practice, however, has been quite slow.
The popularity of the virtual world Second Life during the period 2007--2009 has generated a renewed interest in virtual reality for GIS. Because its build tools are so easy to use, several experiments in urban development and architecture have been made there. Our work in virtualization of urban plans started in Second Life [24], but it soon moved to OpenSimulator [25]. ArchVirtual (Site 8) is an example of Second Life architectural experiments that evolved into a commercial endeavor. ArchVirtual is now using OpenSimulator, so it shares many similarities with the infrastructure presented here. Similar efforts connecting OpenSimulator to GIS are being made by several people around the world (e.g. Site 9, Site 10). To our knowledge, our virtual Uppsala model is the largest and most featurerich urban planning model ever made with OpenSimulator/Second Life.
Also recently, but outside the OpenSimulator/Second Life technologies, UrbanSim (Site 11), particularly its UrbanVision application [37], is the closest work to virtual Uppsala. UrbanVision currently supports a virtual rendition of the San Francisco Bay Area, and is being used by urban planners in that area. It shares many similarities with our system, namely capabilities for 3D modeling and for simulating traffic and pedestrians. UrbanVision is a relatively recent addition to UrbanSim, and is not available for distribution, so we cannot make any meaningful comparisons.
But in spite of the very large body of work in virtual reality technologies for GIS, very few papers exist reporting on actual experiences of use of those technologies in action for the purposes of urban planning. Some papers report on the difficulties of modeling the cities at large-scale, and consequent techniques used for doing so [10]. In our case, even though the area was relatively large, the modeling work was relatively straightforward: we used the well-known paradigm of focus-plus-context [3] in order to speed up the modeling work for the purposes of the plan at hand.
Thompson et al. [36] is, perhaps, the publication that is closest to reporting actual experiences. That paper reports on an ongoing relationship between Northumbria University and the local authorities in order to achieve one single authoritative city model that can be used for a variety of applications. The model is hosted by the university, and the urban planners access it remotely. It is stated that the model is offering many benefits to the local authorities, resulting in time and cost savings, but no further information is provided. The paper reports on the emerging issues surrounding the discovery, reutilization and conversion of existing data, as well as on other non-technical, but equally important, issues of origin and ownership of data. As stated in Section 5.3, we faced similar issues with data acquisition. The paper also mentions the existence of a dedicated point of contact between the University and the urban planners, similar to the process we put in place. In their case, that person is also the modeler. In our case, that person did some modeling at points, but was in no way the main modeler; we found no need to add direct communication between the main modelers in the United States and the urban planners in Uppsala.
The main focus of this paper is the case study of the social process surrounding virtual Uppsala and its role in the planning process of the PRT system, and not the virtual reality infrastructure itself. Because the use of virtual reality cities in urban planning is just emerging, we believe our experiences with the city of Uppsala are valuable pieces of information for others to be able to avoid mistakes and reproduce successful strategies for the benefit of sustainable urban plans.

Methodology
In spite of the substantial body of work related to virtual reality in activities related to urban planning (see previous Section), we could not find any reports of experiences of use in actual real-world projects. This paper presents one case study of the use of a virtual city in urban planning --the PRT project in the city of Uppsala, Sweden --spanning over a period of 4 years. Merriam-Webster's dictionary defines a case study as follows: Case Study. An intensive analysis of an individual unit (as a person or community) stressing developmental factors in relation to environment.
This definition does not establish any specific methodology; it simply implies the scope of what's to be studied. In our particular case, the scope is the virtual Uppsala model that we built (see Section 4) and the group of stakeholders responsible for brainstorming and supporting (or not) such a radical transportation plan. The focus of this study is neither the technology nor the virtual city itself, but the role that they played in the real-world brainstorming and decision-making process. As such, we are interested in qualitative observations and in formulating grounded hypotheses about the value and role of virtual cities within urban planning.
Our approach to this study was fairly opportunistic, close to the grounded theory methodology [13] -although we did not follow the formalities of that methodology. By opportunistic we mean that there was no upfront experiment design and no upfront hypotheses; instead, we took advantage of the opportunity offered in the context of a real business contract in order to take notes and make observations along the way that would allow us to identify the value of virtual cities for the ultimate goal of fostering more sustainable urban plans, and to formulate hypotheses.
The influential Penguin Dictionary of Sociology [1] has, for years, cautioned that [...] a case study cannot provide reliable information about the broader class, but it may be useful in the preliminary stages of an investigation since it provides hypotheses, which may be tested systematically with a larger number of cases. This subordinate view of case studies has been questioned most notably by Flyvbjerg [11], who clarifies several misunderstandings surrounding the status of case studies within social science methods. In spite of taking Flyvbjerg's position on the scientific value of case studies, we agree with the cautionary note that our qualitative observations should not be generalized, and that many more case studies of this kind need to be conducted before concluding that virtual cities help (or hamper) real-world urban planning. We first describe the major events and milestones of the virtualization project, and then explain the data for the observations made later on in the paper.
The virtual reality rendition of the possible pod car system in Uppsala was originally commissioned by the City of Uppsala in 2009. The first deliverable consisted of an area of 750x750 m 2 around the main train station, and the goal was to conceptualize/visualize a possible pod car station in that area. Specifically they wanted to visualize how large groups of people arriving in trains could be served by pod cars. This work complemented several other feasibility studies, all of them quantitative in nature --cost/benefit analyses, traffic and people flow, etc. While these theoretical studies showed that the concept was viable, city officials had some concerns about its operation in practice. That first deliverable was finished towards the end of 2009. Several political and strategic deliberations ensued in Uppsala regarding the pursuit of the pod car system plan. In 2011, a second piece of work was commissioned, this time targeting an area of 3x1.5 km 2 , a considerable portion of the entire city. The goal of this second phase was to conceptualize/visualize how the pod car system would connect the main station to important destination areas such as the Hospital and the University. This second phase was commissioned by the City of Uppsala, the County Academic Hospital and the University Real Estate Company (Akademiska Hus). The second deliverable was finished in April of 2012.
The virtualization and several byproducts of it (videos, pictures) have been frequently shown to the stakeholders -city officials, urban planners, politicians, and real estate developers --throughout the duration of the project, both in individual and in group meetings, as well as in formal and informal gatherings. The data for this case study consists of the feedback and observations collected during those meetings and gatherings. Additional methodological details are presented in Section 5.

Virtualization Infrastructure
The virtualization infrastructure is based on free, open source software. The server side uses OpenSimulator (Site 2), a platform for developing Second Life-like virtual environments. The client side uses one of the multiple Second Life viewers (Site 3). We describe how we have used these open source components.

The Server Side
The area is divided into a 2D grid of 256-meter regions. There are 6 x 12 = 72 regions total. In turn, the regions are grouped in sectors of 3x3 regions, each sector running in a separate simulator. In total, there are 8 simulators for this area (see Figure 2). We use OpenSimulator in a standard grid configuration, with one central Robust server, and with the simulators all sharing the grid resources. During different phases of this project, we placed the simulators in a variety of servers, from our own machines to AWS EC2 (Site 4). We have developed a simple systems administration layer on top of OpenSimulator that allows us to very quickly deploy simulators in whatever servers we need them to be on.

Terrain
With an external toolset, we are able to generate terrains from GIS data, embedded with aerial images. These realistic aerial-image terrains, by themselves, provide a fair amount of immersion, even before any building is modeled. They also give us the footprint for placing the buildings in the scene and for visualizing the roads and vegetation (see Figure 3).

The Build Process
To a large extent, the build process is the same as any build in Second Life / OpenSimulator. We have been using primarily prim buildings, but we also have sculpties and meshes. We have taken a fair amount of pictures of the building façades in Uppsala, and used them to texture the buildings (see Figure 4).
The build process was a collaborative and iterative effort involving a total of 9 people over the 4 years of the project. Modeling work was done only in certain periods of time, not during the entire 4 years. Most of the team that modeled the buildings was in the United States, and did not visit Uppsala. One person (one of the co-authors) was in Sweden and made frequent visits to Uppsala and to the United States. The model of the PRT system was done by an engineer in Sweden using an external program, and following an existing layout plan. That model was then imported into the virtual reality environment semi-automatically. At critical parts of the project, the entire team met inside the virtual reality environment (it supports voice chat) in order to coordinate the work and keep everyone updated about the outcomes of stakeholder meetings. But besides coordinating the work at a high level, very little coordination was necessary in order to assemble the complete virtual reality model. Specifically, there was not much need to exchange pieces of the model over email or shared storage systems, because the virtual reality infrastructure is the data storage and sharing infrastructure too.

Traffic Simulation
We developed a traffic simulation addon that is capable of driving thousands of vehicles all over the virtual area without this negatively impacting the performance of the virtual city. The traffic simulation runs on a separate server. The vehicles go from one end to the other without regards for region or simulator borders. The current traffic simulation/visualization has been developed from scratch, but the intention is to connect this technology to external traffic simulators (e.g. SUMO [4], [7]).
Currently, the hardest part of this simulation is the establishment of routes. The only way to infer the routes is by visual inspection and by insider's knowledge of the traffic flow and signs in Uppsala. Figure 5 (left) shows the waypoints for cars and buses around the station area manually placed on the ground. With areas like this one, 3km wide, setting up the paths that the vehicles use, and the speed limits, is a daunting task. In the future we hope to be able to get this information in some automated manner.
On the positive side, the podcar system, given that it doesn't yet exist, has been much more amenable to automation. We have automatically generated both the tracks and the routes from an existing plan (see Figure 5, right).

Pedestrians
Since 0.7.3, OpenSimulator supports server-side bots that are scriptable in-world. We have used that facility to create over 100 standing/sitting bots and a dozen of walking ones. The standing/sitting bots are very lightweight; the servers can handle hundreds of them. The walking bots, on the other hand, are relatively heavy, as they are part of the physics scene. The walking bots will be subject of substantial improvements in future virtualizations.

Observations and Discussion
The methodological framework described in Section 3 guided our research work. As stated, we did not go into this study with pre-conceived ideas or hypotheses; instead, the main goal was to make observations about the stakeholders' reactions. Based on those observations we can then formulate hypotheses related to the value of virtual cities in urban planning.
In this section we describe the stakeholders' reactions to the virtual city over time, some of the observations we made, and lessons learned during this project. The section ends with a discussion that places these observations in the context of the research goals described in Section 1.

Reactions over Time
The first (smaller) model was presented to transit and railway authorities in Uppsala at the end of 2009. In the past, these authorities had expressed several concerns regarding the timely distribution of people arriving in trains into the pod cars. The results of mathematical simulations had not been sufficient to ease those concerns. The virtual reality model seems to have eased those objections: from being a serious operational issue, the evacuation of riders out of the main station became a non-issue from then on.
Having surpassed those operational objections, city officials and local stakeholders continued their deliberations on whether to pursue the PRT system or not. The next set of concerns had to do with laying out the pod car guideways throughout the historical part of the city, so as to connect the main train station to the main destination areas, namely the Hospital and the University. As such, in this second phase, the city was interested in visualizing the entire system, not just the travel center. Additional stakeholders joined the project, namely the County Academic Hospital, the University Real Estate company and the state-ran Vaskronan Real Estate company. The second, much larger, virtual city model was commissioned in 2011.
For this second phase, a first meeting was held with the entire group of stakeholders in October 2011, followed by several one-on-one meetings with individual stakeholders between then and March 2012. A final meeting with all the stakeholders was held in April 2012.
The goal of the first meeting of the second phase of the project was to explain the virtualization technology for those not familiar with it. Given that the technology allows many people to login and experience the model simultaneously in their own computers, we attempted to do that during that meeting. This was very problematic, as different people had completely different levels of literacy regarding 3D environments. Having no experience with online gaming or CAD tools, several people in that meeting were confused and, therefore, frustrated with the experience. In subsequent meetings, we decided not to do that, and instead drove the meetings with a shared projection of the virtual city on a screen. This worked much better, as it removed all the accidental complexities of people having to use a completely new tool without any prior training.

Social-Technical Context
Cities are complex socio-technical systems. Their planning and evolution, therefore, are also complex and sometimes chaotic processes. Often, scientific and technical arguments are not enough to make decisions. The decisions surrounding the use of public and private resources in urban areas are dominated by key players who have vested interests in particular outcomes, and, because arguments can always be counter-argued, politics always dominates those decisions. In this social context, it is difficult to gear cities towards more sustainable practices, especially those that require non-incremental changes. Even so, it is possible to break through established territories of influence by engaging with those officials who truly believe in their role as public servants and who want to leave a legacy for the common good. That was the case in Uppsala.
Besides the public officials, there also exists a large community of urban planning consultants who, again, have vested economic interests in particular practices of work. One of the things we experienced was how difficult it was to obtain GIS, land use and buildings data, even though we knew that data existed under some of these consultants' supervision. The problems surrounding the availability of data are well known, and several initiatives are being made all over the world towards open data, but there is still a long way to go to bring those ideas to practice in the context of urban data.
Another, somewhat surprising, observation from the process is that there is no need for the virtual city modelers to interact directly, or even meet, the stakeholders --as long as there is a person in the middle who is capable of conveying (a) the tool limitations to the stakeholders and (b) the modeling requirements to the modelers.
In reflecting upon the process followed in this project, it is clear that the virtual model of Uppsala would have been of very little value had there not been a human agent meeting with the stakeholders regularly, getting them engaged with the model on a personal basis without requiring them to learn the virtual reality tool by themselves. The virtual city served as a concrete, tangible, common operating object to start and sustain the conversations across stakeholders; the engagement that the stakeholders developed towards the model made the process of understanding the plan much shorter. But it was the human agency over the model that made that engagement possible. The outcome would likely have been very different had we simply ask them to login to the model and make their own changes, even after training them. This may be a consequence of the lack of knowledge about the tool, and such a person may not be needed once the next generation of video-game-exposed urban planners takes over. In any case, the importance of the lack of proficiency with particular tools, and the effort it takes to train people to use them, should not be underestimated.

Discussion
Section 1 outlined some of the research questions we were interested in investigating in this case study. We discuss what we found in the context of those questions. Q1. What are the hurdles? In our case, we found one of the major hurdles to be the lack of familiarity that urban planners had with 3D immersive environments. That lack of knowledge on how to interact with the tool was a blocking factor that required us to change our approach with the City of Uppsala. Instead of making the tool directly available to the stakeholders, as originally intended, we had to proceed with a tool expert as intermediary. In general these environments are much more complex than the IT tools that most people use, so we expect this hurdle to be a serious issue in the adoption of these environments, at least until these tools are sufficiently simplified or until a new generation of urban planners growing up in the age of video games is in charge. Another, less surprising hurdle was the difficulty in getting the necessary GIS data; this hurdle has been reported many times in other projects, so it seems to be pervasive.

Q2. Who builds the models and who uses them?
In our case, we ended up building the entire model, although originally that was not our plan. This reiterates the importance of the hurdle identified above. In any case, the centralization of modeling was not an issue, as all stakeholders seemed to accept the model as an accurate rendition of the city. That agreement seemed to be more important than the feeling of ownership.
Q3. How do stakeholders interact with, and through, the model? The model seemed to be a good tool for brainstorming ideas. The engagement and enthusiasm during the one-on-one meetings was very high, because the model could be changed online to reflect the stakeholders' suggestions during those meetings. We were particularly surprised when some stakeholders (i.e. Hospital officials) started paying attention to parts of the model that were unrelated to the PRT system in question. We were also surprised when, in the later phase of the project, some stakeholders started using the model for urban design, additionally to planning. Our conclusion on this question is that the potential for serendipity in these virtual cities seems to be quite high.
Q4. Does virtual reality enable new kinds of processes and new levels of engagement, or are the VR tools just better visuals for the exact same old processes? Our observations regarding this question were mixed. On the one hand, the serendipity noted above seems to be a novelty brought to the table by virtual reality. On the other hand, the dominance of the political context in urban planning processes is undeniable, making the value of any single tool quite hard to assess.
Q5. Do virtual cities ultimately lead to better, more sustainable real-world city planning or are they a distraction? In our case, the virtual city was certainly not a distraction. The first piece of evidence for this was the fact that the city requested a second, much larger model after the first small model had been delivered. It was clear that the conversation about the PRT system was using the virtual city as its main driver, and that it had a strong influence in the continuing interest from the stakeholders. If the city of Uppsala decides to apply for funding for this ambitious project, that will be strong evidence that virtual cities are of great value for sustainable real-world city planning.

Conclusions
The road to sustainable cities is full of resistance to change. But without change, sometimes radical change, sustainability, especially in what relates to energy, won't come fast enough. One of the major obstacles to better energy solutions is the lack of tools for envisioning what the future might look like --not in abstract but in the holistic context of each specific urban area: all aspects, all data, interconnected for that particular city. In considering alternatives, it is absolutely critical that the local stakeholders can visualize and, better yet, feel the consequences that those alternatives might bring to their everyday life. Technical expert assessments presented in abstract, even when they point to cost savings and better solutions, do very little to address the anxieties of those in decision positions and of the general public. We posit that virtual reality renditions of real cities, overlaid with the elements of sustainable urban plans, may play a major role in achieving sustainability in existing cities. This is a conjecture at this point, and one that needs a fair amount of research and case studies.
We have presented a case study of the use of a virtual city in the planning of real-world city, Uppsala, Sweden. City officials in Uppsala have been considering the implementation of a solar-powered Personal Rapid Transit system connecting the main train station to the main destination areas of the city. In the context of those deliberations, they have commissioned the development of a virtual Uppsala overlaid with one possible PRT deployment. The model is fully interactive and consists of structural (buildings, roads, etc.) and dynamic (traffic, pedestrians) aspects.
During the 4 years that we have been involved with this project, we have observed the role that the virtual city has played in the evolution of the conversations between the stakeholders. Whereas in the beginning the PRT system was the object of technical and operational concerns, over time, and partly due to their interactions with the virtual model, those concerns disappeared. Towards the end, the concerns of the stakeholders shifted towards the design of the tracks and stations, and how to better blend them with the city. We observed that the artifact in itself would probably be of very little value, had we not have a dedicated person in place for exercising it during stakeholders meetings. Finally, we also observed that the fact that the model was online and changeable during meetings had a strong positive effect on the stakeholders' engagement with the virtual city, and on their decision to support further efforts to gather political support for the PRT system at the county level. The virtual city is now starting to serve as a common operating picture for urban design.
This case study is just one data point and should not be used to draw general conclusions regarding the role of virtual cities in urban planning. We hope our experience reported here can be reproduced by others so to gather additional evidence on the benefits of virtual reality in sustainable urban planning.