Mae cerbydau trafnidiaeth gyhoeddus fel arfer yn fannau caeedig. Os yw trên neu fws yn llawn, ni all bobl ddewis peidio â mynd arnynt os mai dyna’r unig ffordd sydd ganddynt o gyrraedd y gwaith.
Public transport vehicles are usually enclosed spaces. If a train or bus is crowded it may not be possible for people to choose not to get on as it could be their only route to work.