On most public transport systems, there are at least some activities passengers are prohibited to engage in. Activities like these, which can be restricted in vehicles, stations, and other property of the agency, are prohibited for a variety of reasons. These include keeping other passengers safe and comfortable, protecting the operator, or protecting the vehicles and stations.
Many local public transport services, such as municipal bus or rapid transit systems (one notable exception being the New York City Subway), prohibit passengers from consuming food or beverages or carrying open food or beverage containers while on board a vehicle or in a station.
Generally, services providing longer forms of transportation, such as regional rail or intercity buses, will allow at least some eating and drinking. But some services, like Megabus, prohibit eating and drinking.
In emergency cases these prohibitions may be waived. The Washington Metropolitan Area Transit Authority has a strict ban on consumption of food or drink in the paid area of train stations, on trains or buses, or on elevators or escalators used to enter or exit stations, in order to reduce attractiveness to insects and vermin. Fines of $100 can be imposed, except the Authority has lifted the ban with respect to consumption of water during heat emergencies.
Smoking is one of the most common prohibitions on board a public transport vehicle. Since second-hand smoke can be hazardous to one's health, smoking is prohibited in most public places worldwide, including public transport.
Note that as of 2016, the prohibition on smoking only applies to cigarettes which burn something that generates smoke (e.g. tobacco or marijuana), although some localities want to ban public smoking of electronic cigarettes.
Some intercity bus services will stop to offer smoke breaks to riders.
Most systems prohibit the use of audio-producing devices, such as radios, CD players, MP3 players, musical instruments, or other similar gadgets without an earphone through which only the listener can hear.
Some public transport systems prohibit or limit the use of mobile phones while on board.
Some rail systems have "quiet cars" where passengers are not permitted to engage in conversations and where cell phones cannot be used.
In some places, it is unlawful to photograph or film a public transport vehicle or station or the operation of a public transportation service.
Anti-photography laws (or rules) are in place for various reasons, including the privacy of passengers and crew and concerns over terrorism. However, these measures have caused problems for enthusiasts whose hobby is to ride and photograph transport. In some cities, the rules have been abandoned or modified. In other places, the authorities regard enthusiasts as their supporters and encourage their activities so long as they are carried out in a lawful manner from places open to the general public.
In the United States, it is generally legal to take photographs in public, and absent special and extraordinary conditions, a law prohibiting photography in public areas of a transit vehicle or area operated by a transit authority, or a transit authority prohibition on photography under such conditions likely would not withstand judicial scrutiny, and the courts probably would not uphold such bans.
Many systems have anti-solicitation laws or guidelines. These include prohibitions against:
Some services have guidelines regarding the amount of space a passenger can take up whether with one's body or belongings.
In some transit systems, including the New York City Subway, it is unlawful to place one's belongings on another seat, even when vacant; however, in the New York City Subway, this rule is flouted all the time.
Privately run intercity bus services usually have limits for carry-on and checked luggage, similar to the baggage allowance system on airplanes.
Some transit systems have a seating precedence rule for passengers who pay adult fare against discounted passengers, i.e. discounted and free-pass holders may not sit unless all adults paying full-fare sit.
While any crime committed on a public transport system would generally be treated like one committed elsewhere, there are some acts for which the prohibitions are emphasized in guidelines on posted signs.
Generally, firearms, in countries where they are otherwise allowed to be carried by civilians, are not permitted on board public transport vehicles. Exceptions can be made for law enforcement or military personnel or others with a carrying permit.
Many systems prohibit explosives and flammable liquids that pose threat to the safety of others.
Many places prohibit live animals from being brought on board public transport vehicles. Exceptions are sometimes made for animals kept within a container from which they cannot escape or service animals for those with disabilities.
On most rail systems, bicycles are allowed, but may be restricted. On buses, there are more such limitations.
Many buses now have external bike racks where riders can attach their bikes.
Sometimes, bikes are only allowed on buses if there is enough free space.