The term rapid transit refers to fast public transport in and around cities, such as metro systems.
Funding for public transport systems differ widely, from systems which are run as unsubsidised commercial enterprises to systems that are free of charge:
One reason many cities spend large sums on their public transport systems is that heavy automobile traffic congests city streets and cause air pollution. It is believed that well maintained, high volume public transport systems alleviate this. Many complex factors affect the outcome of spendings in public transport, so success in reducing car traffic is not always assured.
Another reason for subsidies for public transit are the provision of mobility to the disadvantaged who cannot afford or are physically incapable of using an automobile.
Public transport can be faster than other modes of travel; prime examples are in cities where road congestion can be avoided, and for long distance travel where much higher speeds are possible than are permitted on roads.
Forms of public transport (in the broad sense):
Some of these types are often not for use by the general public, e.g. elevators in offices and apartment buildings, buses for personnel or school children, freight trains, etc.
Rail transport systems tend to be favoured by many cities.
Public transport is sometimes used by homeless people and budget tourists as a sleeping place. This can vary from the tourist who travels on purpose at night in order to sleep while travelling and dispense with the cost of a hotel, to people for whom the 'sleeping accommodation' is the purpose, and the displacement of the vehicle a somewhat inconvenient side-effect.
For the latter a requirement is that riding a whole night costs less than a hotel. This may especially be the case with a rail or bus pass.
One popular example is the Santa Clara Valley Transportation Authority (VTA) bus route 22, dubbed 'Hotel 22', between Palo Alto, California and San Jose, California, (Silicon Valley). A pass for 24 hours costs 4 dollars and one for a month 45 dollars, much less than a hotel, house or apartment.