During the last decade the available data increased exponentially thanks to more affordable electronics and a more powerful computational power, allowing to extract fundamental features or making predictions. During the 2019 pandemics, due to monitoring needs, many public transport operators had to install cameras or other sensors to count the people flow and monitor their temperature. The data coming from those systems can be easily extracted and analysed also for other purposes, such as congestion monitoring, a theme that has a long history in the transport field; it allows both to save money related to personnel and to continuously monitor the state of operation, avoiding the human errors.