The COVID-19 pandemic has changed people's lives in greater or lesser degree since the outbreak back in December 2019 in Wuhan, China. Due to the high transmissibility of the virus and with the aim of preventing the virus from continue spreading, several measures have been applied during the last two years, which now have become part of people's daily life. One of these measures is physical distancing, which has been proven to be an effective way to reduce the transmission risk. The objective of this research is to understand how the walking behaviour of pedestrians has changed during COVID-19 because of physical distancing at bidirectional flows in locations where people might encounter difficulties for complying with this measure, and conduct a calibration of the pedestrian simulation model Pedestrian Dynamics (PD) to improve its accuracy for reproducing such behaviour. As a result, this research aims at determining the capability of the model to reproduce the walking behaviour during the pandemic. The results show that the walking behaviour has changed over the course of the pandemic, since in 2020 and 2021 pedestrians kept respectively larger and shorter distances than in 2019. Moreover, a larger variability in velocity and higher effort to traverse the measurement area suggest changes in the awareness of their surroundings during the pandemic. The calibration results show that the relaxation time is the most relevant parameter as the accuracy of the model significantly changes when values lower than its default are used, which in turn indicates a faster reaction of pedestrians. In conclusion, a calibrated model considering one parameter would not yield accurate predictions if a general usage for all COVID-19 scenarios is intended. Finally, different types of behaviour are recommended to be analysed to obtain insight into the capability of the model to reproduce them and moreover, the behavioural assessment at strategic and tactical level are adviced, since this research focused on the impact of physical distancing on the behaviour at operational level.