Are digital twins the future of urban planning?
Like any city, Boston is constantly changing. Old buildings crumble, new ones rise. Public transit winds through the city. Everything from schools to grocery stores to trees dot the landscape.
For years, the city wanted to capture it all in a 3D digital model that could help guide planning decisions before they took effect in the real world. This model was born in 2015, and three years later the city did publicly available.
This digital twin encompasses the current landscape of buildings, public transport, trees, daylight and shadows, and points of interest. It also contains proposed and under construction buildings and serves as an archive of what Boston has looked like over the years.
“It’s like a living, breathing type of content in that it’s archival, has current and then has future,” said Carolyn Bennett, deputy director of GIS, or system mapping. geographic information, for the Boston Planning and Development Agency. “It kind of covers the gamut, and I think it’s helpful for the agency and the city of Boston as a whole.”
Digital twins, virtual 3D replicas of a system, place or thing, allow cities and owners to test changes before applying them in the real world. Cities of Los Angeles at coastal texas and beyond are increasingly using this technology to study the effects of development, traffic, climate change, and a myriad of other situations a city faces.
“You can simulate the effects of your decisions on a physical object, in this case a city or a campus, before actually making those changes in the real world,” said Ankit Srivastava, associate professor of mechanical and aerospace engineering at Illinois Tech. “It makes decisions much more data-driven and much less expensive because you can play around with various possibilities.”
But it takes time and effort to ensure a digital twin stays up to date and helps a city move forward.
Capturing a city in the digital realm
Since 2005, Boston has had conversations about how to fit the city’s data treasures into a 3D model, Bennett said. Data available included geospatial data for water and sewer, transportation, tax packages and more.
Now Boston’s digital twin contains this library of data. The city can use it to review development proposals and their effects on a neighborhood in terms of housing, zoning, and parking. Planners can take urban heat island data from other sources and overlay it on the twin to visualize temperatures with reference to buildings, impervious surfaces, and treetops, for example.
“It’s a better way to kind of visualize what we do as planners,” Bennett said. “We plan in 3D. We’re not a 2D agency. We look at the world in its existing form, so you kind of have to look at it in 3D.”
Chattanooga, Tennessee, has also found a digital twin to be a useful tool for encompassing the data it collects.
“Can we bring all this data together in real time in a common ecosystem, where we can get a really good picture of what’s going on?” said Jibo Sanyal, who leads the Computational Urban Science Research Unit at Oak Ridge National Laboratory.
Researchers from Oak Ridge and the National Renewable Energy Laboratory have teamed up with Chattanooga to create a digital twin that helps anticipate and reduce traffic congestion. Sanyal is the technical and strategic manager of the project.
Information from 500 different sources, such as traffic cameras, 911 data, radar detectors and weather stations, feed Chattanooga’s digital twin. Traffic congestion experiments performed in this virtual domain have shown up to 30 percent improvement in traffic flow, which translates to greater energy efficiency, Sanyal said.
Researchers are using the results of these digital twin experiments to bring change to the real world. For example, transportation planners typically collect data during morning and afternoon traffic peaks. But when researchers conducted digital twin experiments on Shallowford Road in Chattanooga, they found that more than 90% of cars were stopped by red lights during the midday rush.
In the real world, these researchers used knowledge from these experiments to recalculate the timing of traffic lights along Shallowford Road to reduce congestion. They can now change their signaling pattern every four minutes depending on traffic conditions, Sanyal said.
Chattanooga has one of the busiest freight corridors in the country, so the digital twin also enables longer-term decisions. For example, the city wanted to know if there are certain times of day when it makes sense for drivers to use the shoulder as a travel lane? Using a digital twin for this work reduces evaluation costs, Sanyal said.
“A lot of research really stops [when] they publish a good article, often a very compelling article, but the opportunity to implement it in the real world is often not there,” he said. “Chattanooga is amazing. In fact, they let us come in and work with them to change their traffic light settings, configure them slightly differently if needed, and run these experiments in the real world. And then we observe before and after to determine what kind of improvements we see.”
Although the researchers are currently only monitoring signals along a corridor, Sanyal said he expects them to monitor about 100 signals within a year, in downtown Chattanooga and throughout other high traffic areas of the city.
The buildings that make up a city
Digital twins can also help cities and homeowners reduce their energy consumption.
cities produce about 75% global greenhouse gas emissions. To reduce this pollution, cities such as New York, Boston and Washington, DC have created goals for a future where buildings have net zero carbon emissions.
But decarbonizing a building requires analyzing and implementing energy management systems and renewable strategies, in addition to purchasing carbon offsets. Cityzenith is one of the companies focused on developing urban digital twins that help do just that.
The model can start with as few as two to five buildings, CEO Michael Jansen said. Owners input their data using a model, and the resulting digital twin helps them run and optimize simulations based on factors such as a building’s age, condition, and destination . The objective is to have buildings and therefore cities that are more energy efficient.
Las Vegas and New York have adopted this technology, Phoenix and other US and European cities are expected to follow. Cityzenith plans to donate the technology to a total of 10 cities by Christmas this year and a total of 100 cities by 2024, Jansen said.
Barriers to digital twins
One of the biggest hurdles to implementing digital twins is making sure all the necessary data is in place to build the model, Jansen said. “Digital twins can’t be bought,” he said. “They are built.”
Due to the amount of data major cities already have, more are expected to use digital twins, said Mohammad Heidarinejad, assistant professor of architectural engineering at Illinois Tech. He added that in five to 10 years, these models could also make their way to smaller cities.
But cities and landowners will face obstacles along the way. Capturing reality with a drone or scanner requires a lot of storage, and a digital twin needs to evolve over time as things change in the real world, Heidarinejad said. (Boston updates its model twice a year.)
One way to update a digital twin is to collect data, including photos that people take of a city and agree to contribute to the project, said Srivastava, of Illinois Tech. Perhaps a central system could analyze those photos and their GPS coordinates and automatically update the digital twin with that information, he suggested.
The data contained in digital twins can pose privacy issues. If people can access the information behind a twin, hackers can too. Srivastava said a city has to decide how much detail to capture in its digital twin and what to make public, especially as the amount of data in the world increases.
“There’s going to be more and more real-world virtualization, and it’s only because it’s so much easier to get data,” he said. “I think this is going to be leveraged in the future by cities.”
This will likely require investment from cities. Bennett said Boston has a 3D data analyst on staff whose primary responsibility is the city’s digital twin.
“Cities need to commit to this because it’s living content and data that you need to keep up to date and maintained,” Bennett said. “It’s a challenge that way because if it gets too stale then people really win. I don’t want to use it.”
Oak Ridge National Laboratory’s Sanyal said staffing and IT overhead can be difficult for a city. After all, cities want to be good stewards of taxpayers’ money, so they tend to use things that are proven to work.
The digital twin work Oak Ridge has done with Chattanooga is designed to help with that. Oak Ridge focuses on solutions designed to adapt to other cities. Sanyal therefore wants companies to license the technology from the national lab.
Still, a digital twin is just one tool cities and properties can use to chart their future, and the value it can provide will largely depend on the data it has to work with.
“Because it’s so data-driven, it’s also really important to be careful about the data we bring in to make those decisions,” Sanyal said. “Ultimately, a digital twin is a tool, and large-scale planning decisions are usually made by humans.”