‘It’s a personal decision’… How should we end up wearing masks on trains? A conclusion drawn from the data by a professor of the University of Tokyo

Train travel was still involved in the spread of corona infection.

The wearing of masks has been left to individual judgment since January 13. The guidelines provided by the government as a reference for judgment recommend wearing masks on crowded trains and buses during rush hour.

However, the “Railway Liaison Committee,” consisting of seven JR companies, private railways, subways, and other organizations, revised the guidelines for infection control and deleted the section on urging passengers to wear masks. Railroad companies have stopped calling for the use of the device through in-train announcements and posters.

In short, it is up to the individual to decide. But what in the world should we base our judgment on?

Professor Yukio Osawa of the Graduate School of Engineering at the University of Tokyo, who has been involved in measures to prevent corona infection as a member of the Cabinet Secretariat’s research and development team, has drawn conclusions based on data analysis and simulations. We asked Dr. Osawa about the risk of infection on trains.

Does “be careful” mean that trains are still dangerous?

There has been a theory that trains are relatively safe,” said Dr. Osawa. The doors open frequently, there is constant ventilation, and passengers wear masks and ride in silence. So it is not so dangerous. That said, there was no evidence that the infection was not spreading on the train.

I concluded from the Agoop point-of-use data that the risk of infection is still high on trains. The human flow data I used is data on the location of individuals obtained from a smartphone application in the 62 wards, cities, towns, and villages of Tokyo, allowing me to determine the speed and direction of movement.

This data shows that there is a correlation between the speed of human movement and the number of infected people.

He said, “To put it a bit crudely, if the correlation coefficient (a measure of the relationship between two types of data) exceeds 0.4, it is said to be so-so correlation. The correlation coefficient between the speed at which a person is moving and the number of infected people that we can assume would be on the train is 0.56 in the winter of 2020, which is high enough.

People walk at a speed of about 1 to 1.5 meters per second, but in the winter of 2020, the number of infected people will be higher in areas where the average speed of travel is 2.0 meters per second or faster. This is a time when the number of people using trains during rush hour in the metropolitan area is 60-70% less than before the COVID-19 crisis, so if we assume that about 1.5 percent of people traveled by train or other means, the average speed of travel would be about 2.0 meters per second.

In the summer of 2021, however, the number of infected people is decreasing as the speed of people’s travel increases. Moreover, the average speed of travel is about 4.6 m. It is reasonable to assume that the very large increase in the use of private vehicles between 2021 and 2020 is the reason for the increase in average speed.

As we have already shown in our previous studies, the risk of spreading infection is lower when passenger cars are used. So this fact leads us to believe that the increase in the number of infections in the winter of 2020 was due to the use of trains and buses.”

Wear masks around terminal stations where diverse people congregate.

Dr. Osawa also presented his findings on the Cabinet Secretariat website regarding “stations” where people gather to use “trains. In order to derive what kind of stations are most likely to spread infection, he himself devised a numerical value called “direction-of-movement entropy. This is said to indicate the variation in the direction in which an individual with a smartphone heads. Incidentally, Dr. Osawa is the first person to have created data on the relationship between “direction-of-movement entropy” and the number of people infected with coronas.

The analysis showed that municipalities with greater variation in the direction in which people move have a higher risk of infection. The correlation coefficient reached 0.78 in the winter of 2020 and 0.89 in the summer of 2021.

In each town, the station is the place where the greatest amount of human traffic occurs. Diverse people from many directions gather at stations in the morning and disperse from the station in many directions at night.

However, the directional entropy of movement is quite different between terminal stations such as Shinjuku, Ikebukuro, and Shibuya stations and the nearest station to the University of Tokyo. In the case of the station closest to Todai, the majority of people who get off the train walk toward the university. Since the directional entropy is low, the risk of infection is low. On the other hand, terminal stations have people moving from many directions to many directions. So the risk of infection is high at such stations and in the vicinity of the station.

In a terminal station, there are many people who take the train home after enjoying food and drink. It is certainly safer to wear a mask.

It is a good idea to wear a mask from the time you are on your way to the terminal station. I think it would be safer to wear a mask from the stage when you are heading to the terminal station. Some people may think that they are safe on the train because they don’t talk to other people, but they can never be assured of safety. We have results showing that infections spread on trains, so I think it is better to wear a mask during crowded times.”

The idea that all we have to do is listen to the government is wrong in the first place.

By the way, will the Cabinet Secretariat’s simulation project that Dr. Osawa is involved in continue in the future?

I personally hope that it will continue, since the project for social implementation started this year. For example, we are holding workshops for residents of municipalities, asking them to think about what they should pay attention to and bring the results back to their communities. This kind of experiment is what is needed. The idea that all we have to do is listen to what the government says is wrong.

Japanese people are not able to make up their own minds about wearing masks, saying, “I want the government to set the criteria,” or “I will go along with the people around me.

Even after the 13th, everyone is wearing masks,” he said. I often hear people say, ‘Because the people around me are wearing masks,’ but it is important to make a more reasoned decision.

According to a nationwide telephone poll conducted by Kyodo News from November 11 to 13, 56.8% of respondents said they would “continue to wear masks as before. How long do they plan to continue wearing them? ……

The respondents said, “I will wear a mask in places where I need to be careful, such as on trains and around terminal stations. I believe one should wear it on and off in a crisp and clear manner based on one’s own judgment.”

Yukio Os awa, Professor of Systems Innovation, Graduate School of Engineering, The University of Tokyo, was born in Kyoto in 1968. He has been in his current position since 2009. He specializes in system design, knowledge engineering, and business science. His research interests include opportunity discovery, innovation markets based on data jackets, and visualization and valorization of data.