We first created anew mathematical methodcombining compartmental models analyzing the transmission of infectious diseases with pedestrian models and studied the case of individuals moving in a corridor. We then decided to apply this method to investigate the transmission of generic airborne infection in a specific crowded and confined environment. Because passengers have set trajectories, underground stations can be imagined as long corridors from the entrance point to the platform and, vice versa, from the train to the exit.
How did you come up with the study design of combining oyster card data and Public Health England data? What did you hope to find?
We hoped to validate this method by finding a correlation between the total number of people entering and exiting the underground and the time taken to walk towards the platform (or towards the exit) i.e. at higher densities, crowds move slower and it takes longer to reach the final destination.
What did your results show?
Results show that there is a correlation between the use of public transport and ILI rates in London. In particular, in boroughs that have a higher than average number of ILI cases, the number of contacts residents make when travelling is higher. This is because they need to stop multiple times during their trip in order to change lines. On the other hand, people that live in well-connected areas, who are served by more underground lines, make faster trips because they do not have to stop in crowded junctions such as King’s Cross St Pancras or Victoria Station, and thus they get in contact with a smaller number of individuals. These results are in line with other environmental and demographic factors such as age, population density, employment and income.
Avoiding travelling during peak hours and limiting the changes of line would reduce the risk of exposure to contagion.
On a public level, flexibility in travelling times and routes is important. Avoiding travelling during peak hours (generally 7:30-9:30 am and 4:30-6:30pm weekdays) and limiting the number of line changes would considerably reduce the number of contacts and, consequently, reduce the risk of exposure to contagion. From a policy-making point of view, this research has the potential to inform future station design, ventilation systems and pedestrian routes.
What do you expect to investigate in the future?