‘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.”