The concept of "safety" can be understood in very different ways, depending on whether we are considering public transport (bus, metro, tram, etc.) or private vehicles. One of the advantages of public transport is that users do not have to worry about tasks such as driving, navigating and monitoring the vehicle’s surrounding environment. They therefore often feel safer on public transport than in a private vehicle. However, the downside of this feeling of safety is that accidents on public transport can be especially traumatising for passengers – all the more so given the likelihood of there being many victims.With regard to safety and security measures: although certain modes of transport, such as air travel, may be subject to considerable monitoring mechanisms, such measures are much more complicated to implement in the case of urban public transport, where a great deal of flexibility is required and where high flows and speeds must be maintained. Consequently, the main security measures currently used involve reinforcing a human presence and installing video surveillance systems. These two measures also have an effect on "petty crime", which is a factor that dissuades many people from using public transport out of fear of abuse or attack. Increased surveillance must therefore not only take place within the mode of transport itself, but also at stops and interchanges.