Media release: Poor ventilation on buses and trains – a fixable risk to health

Poor ventilation on our buses and trains is leading to an increased risk of passing on respiratory infections such as Covid-19, according to new research.

The latest Briefing from the Public Health Communication Centre details the results of testing on public transport from April to June. The research measured carbon dioxide (CO₂) levels in air as a marker for poor ventilation. When more than half of the seats were occupied, poor ventilation was recorded 94% of the time on buses and 77% on trains. These results show that passengers in these buses and trains are doing a lot of re-breathing of other people’s exhaled air.

There was also a clear pattern of increasingly poor ventilation as seats got filled up and especially if passengers were also standing in aisles of buses.

Lead author, University of Otago Professor Nick Wilson says he was a little surprised by how high some of the results were. “They were up to eight times background levels (eg 3440 parts per million [ppm] of CO₂ in a crowded bus vs outdoor air at 417 ppm). But even so these findings were generally similar to other New Zealand research and international studies in public transport settings.”

Professor Nick Wilson says research around Covid-19 has led to a more sophisticated understanding about ventilation and how it can help protect us from airborne viruses. “We need to take advantage of that knowledge and take action to improve ventilation in indoor settings.”

He says there are a series of measures which could lessen the risk including developing a common set of national air quality standards for public transport. “These have been suggested to the Government by the Wellington public transport network Metlink and are a very basic requirement for a safer transport system.”

Professor Wilson says transport companies and local and central government also need to be looking at recommendations for improving ventilation, ranging from actions such as opening all bus/train doors at each stop, to improving the built-in ventilation systems on buses and trains. “There are other big fixes like increasing public transport services so there is less overcrowding, improving walking and cycling infrastructure, varying work start times more to ease the rush hours and allowing working from home. This is a problem that could benefit from a wide range of actions.”

“We also identified relatively low mask use by passengers in buses and trains during our study – in the 3% to 11% range,” says Professor Wilson. “We need government funded studies on public knowledge and attitudes to mask use to inform current day use and for future pandemics. But that should be alongside a concerted effort to improve ventilation on our buses and trains now.”

The researchers say until improvements are made, commuters who want to avoid infections should use masks and even avoid travelling on very crowded public transport. “Requiring buses and trains to monitor and display continuous indoor CO₂ readings on screens could help passengers make informed decisions about when to wear masks and the timing of their travel.”