Coronavirus graphic with map

Transportation networks and viral spread

CSE professor using transportation data to better model COVID-19 spread

In a normal year, Raphael Stern would be studying the impact of self-driving cars on traffic flow—specifically, how these patterns will change in the future as society uses more autonomous vehicles. This year, the College of Science and Engineering assistant professor is putting his efforts into a more immediate problem: COVID-19.

When the pandemic began in the United States in March 2020, universities across the country were on spring break, and thousands of people were traveling from state to state. Stern, a faculty member in the Department of Civil, Environmental, and Geo- Engineering (CEGE), saw a connection between his area of expertise—transportation—and the spread of the novel coronavirus. Now, Stern is working with Philip Paré, an assistant professor at Purdue University with experience modeling diseases, to explore how the virus spreads via transportation networks, mainly commercial flights.

“We had this idea to integrate real-time transportation data into some of these virus spread models to try to model COVID,” Stern said.

“We thought it would be really interesting to see if we could try to collect that data and better understand how the virus is spreading.”

Countrywide connections

In order to predict patterns of infection, many viral spread scientists use what are called SEIR models, which categorize people as being S (susceptible), E (exposed), I (infected), or R (removed, or no longer likely to be infected). Stern and Paré are using a version of this—network SEIR models—which focus on how the virus can spread within a specific county and to nearby counties.

“Imagine you’re in one county, and there are only a few people sick there,” Stern explained. “But, there are a lot of people sick in a neighboring county, and there’s a chance you’ll have some sort of contact with those people. Then, your chances of getting sick in your county go up.”

That’s an example of monitoring spread on a local level, but Stern and Paré wanted to study long-range spread of the virus. The researchers received a National Science Foundation RAPID grant in March and have since been gathering data on every single commercial flight in the U.S. dating back to January 2020. This information ranges from the number of flights to how many seats were occupied on each plane.

Stern’s team, which includes CSE Ph.D. student Mingfeng Shang and undergraduate student Joseph Pham, are responsible for collecting the transportation data. Paré’s team then integrates it into their virus models. With the added transportation data, the researchers found that they could more accurately monitor viral spread—and, they found a close correlation between how much people are traveling and the spread of COVID-19.

“What we found is that we’re better able to predict the number of people who are infected in urban counties if we take travel into account,” Stern said.

“In rural counties, it doesn’t really make a difference, and that’s probably because most of the people are traveling into urban areas to fly,” he added.

The researchers are still collecting data, but their ultimate goal is to provide insight into how travel restrictions have impacted virus spread. 

Localizing the effort

Stern has begun a similar study with fellow U of M civil engineering assistant professor Michael Levin. This time, focusing on viral movement within Minnesota. Using data from the Minnesota Department of Transportation, they’re studying changes in the volume of road traffic within and across two or three regions in the state. Their findings could guide transportation policy during COVID-19 or even in the event of another future viral outbreak.

Stern is also advising Shang and another student as they explore how traffic changed during the quarantine. Data shows that traffic volumes in the Twin Cities were down 40 percent overall at the peak of the quarantine, but just what does that dip mean? Does it, for example, compare to a large snowstorm? Their project seeks to understand just how unusual that dip was compared to other traffic interruptions.

Stern said it’s been exciting to find that his area of expertise, transportation data, can be applied to modeling and understanding COVID-19.

“For me as a transportation engineer, it’s kind of cool to be involved,” he said. “Most people would say [the pandemic] is just a public health thing, but I think it also highlights how interconnected engineering disciplines, especially civil engineering, are.

"Transportation engineering is not only about getting people from one place to another, but there’s also a public health aspect involved."

While COVID-19 poses many challenges, Stern believes it has also provided opportunities for engineers to adapt and come up with innovative solutions.

“I think across the college and across the University, a lot of people retooled their research,” he said. “Humanity was hit with a major crisis, and we all tried to figure out how we could contribute. As engineers, that’s what we do. We try to solve problems related to how we can make our world better. COVID-19 provided a lot of opportunities to rethink our world, and engineers rose to the occasion.”

Read more about Stern’s work on transportation and COVID-19 spread in Minnesota.

Story by Olivia Hultgren with excerpts from a CEGE Magazine story by Merry Rendahl