Good air in buses and trains

TU Berlin and ICM of Charité investigate aerosol dispersion in public transport vehicles quantitatively on behalf of BVG

Public transport in Berlin remains safe even during the Corona pandemic - for passengers and drivers. This is the result of a recent study by the Department of Experimental Fluid Mechanics at Technische Universität Berlin and the Laboratory of Biofluid Mechanics at Charité - Universitätsmedizin Berlin. A team of scientists led by Prof. Dr.-Ing. Christian Oliver Paschereit and PD Dr.-Ing. Ulrich Kertzscher was commissioned by the Berliner Verkehrsbetriebe (BVG) to experimentally investigate the dispersion of aerosols in various Berlin subways, streetcars and buses.

For this purpose, the researchers used artificial theater fog as well as aerosol measurements in which virus-laden breathing air is simulated and inhaled by human-like mannequins. In this way, they were able to determine that vehicle ventilation and the targeted opening of windows and doors were effective in reducing aerosol concentrations by up to 80 percent. The study did not include the additional, positive influence of medical masks, such as those currently worn by passengers.

The volume of a bus, for example, is roughly equivalent to that of a medium-sized conference room. Opening the doors at each stop would be comparable to opening the windows every minute and a half or so during a meeting. In addition, passengers on public transport often spend only a few minutes in the vehicles.

Prof. Dr.-Ing. Christian Oliver Paschereit, Head of the Department of Experimental Fluid Mechanics at the TU Berlin: "We were very pleased that our newly developed measurement technique could contribute to assessing the dispersion of aerosols in public transport and thus the risk of infection with SARS-CoV-2. We were able to show here that the ventilation systems as well as the opening of windows and doors very significantly reduce the aerosol concentration in the means of transport under consideration."

PD Dr.-Ing. Ulrich Kertzscher, head of the Laboratory for Biofluid Mechanics at Charité: "It was an exciting challenge to use our measurement system in the different types of vehicles in driving operation. The fact that the measurement results turned out to be so positive actually surprised us, but of course also made us very happy. As expected, measures have to be taken, but opening the windows and doors in combination with the ventilation systems in the buses and trains significantly reduce aerosol dispersion."

Eva Kreienkamp, CEO of Berliner Verkehrsbetriebe (BVG), said, "I am very pleased that this study now confirms to all our passengers and employees*: using buses and trains does not pose an increased risk of infection. With masks, distance and good ventilation, we can continue to travel safely together."

Dr. Manuela Huetten, head company physician and pandemic officer at BVG: "It was a particular concern of ours that the effectiveness of the separating discs in our buses should also be scientifically tested under Corona aspects. Unlike in the subway and streetcar, our driving personnel in our buses do not sit in a cabin. The study shows that the newly installed separating discs effectively prevent the spread of aerosols from the passenger compartment to the driving personnel and shield them well. In combination with driver compartment ventilation, this results in maximum workplace safety from an occupational health perspective."

Despite a demand of currently only about 45 percent of the comparable pre-Corona periods, BVG buses and streetcars continue to run the full range of services, in school transport and on a number of bus lines even with additional services. This means that there is particularly ample space in the vehicles. Where technically possible, the doors of trains and buses open automatically at all stops. The findings from the study are now being used to apply ventilation and window opening in the individual vehicles in an even more targeted manner to reduce possible aerosol concentrations.

More detailed information on the measurement method used: https://www.tu.berlin/en/about/profile/press-releases-news/2020/oktober/sars-cov-2-new-measurement-technology-enables-risk-assessment/

BVG press release: https://unternehmen.bvg.de/pressemitteilung/gute-luft-in-bus-und-bahn/

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