Player can legitimately use a publicly accessible travel system. Especially NPC piloted systems that are regulated and/or funded by a government or co-op
The first video game about Public Transit was released in 1982.
Trains, buses, and subways obviously. Almost always something triggered by a schedule or continually reoccuring circumstances that (by implication) continues to operate with or without the players use of it (even if the player never actually sees this happen). But rarely if they are military in nature, privately owned, or chartered. For instance, Taxis are chartered and generally do not have a set schedule (although they are continually triggered by reoccuring contitions). Also be on the lookout for airlines, air ships, a network of transport cannons (fantasy transit is acceptable, but not chartered flights), public teleporters (sci-fi systems are ok), a series of tubes (like in Futurama), a public bicycle system, and so on. A schedule is not strictly required, public use, even if implied and not seen, is more relevant. Systems that only include a certain group are not exactly public. Such as, trains and buses based within a theme park. Since only theme park customers use these. Ski lifts also are not public transit, unless residents use them to travel to work or home too. A ferry, if it is public. Elevators probably don't count unless they go to a different building or something unusual like that. Hitching a ride, such as Spider-man sticking to the el-train, does not count, unless he has a prepaid pass, buys a ticket, or is otherwise specifically authorized to do this.