Customs and habits of usa

Elderly and Disabled: Federal law and some state and local policies require front seats on buses to be vacated for the elderly and disabled passengers. On subway cars, seats located nearest to the doors are designated for this purpose as well. It is also respectable to permit elderly and disabled passengers to exit the vehicle first as a sign of courtesy and respect, and to permit them additional time to exit the vehicle safely.
Pregnant: If a lady is obviously pregnant and needs assistance getting on or off of a bus or train, it is considered polite to help her, especially if she is carrying bags or the like; on large public buses (like those in New York City) similar rules of etiquette apply as if she were elderly (it is considered polite to give up one's seat so she can sit down.) When in doubt as to whether she wants assistance, ask her first and then proceed. Make room for her if possible: remember, she is carrying something much more precious than just a grocery bag!
Seating: Passengers should extend courtesy by not taking more than one seat on the vehicle, and especially in situations where the vehicle is crowded. Passengers sitting at a window seat with a passenger sitting in the aisle seat, and requiring to exit should have the passenger in the aisle seat stand up and move away from the seat to permit exiting. In no fashion is it proper for an aisle seat passenger to turn to their side.
Standing: On buses with front door boarding, it is typically required for passengers to move to the rear of the vehicle to allow the most passengers to board the vehicle. Passengers sometimes fear it is not acceptable to move to the rear of the bus as it has been stereotyped that the rear of the vehicle is common for "thugs" and other non savory people; while some people believe in this stereotype, this may be an advantage to find an open seat. In a situation where passengers do not move to the rear and stay within the first half of the bus, the driver may assume the entire vehicle is full and cannot pickup any more passengers, thus making passengers at stops become frustrated and forcing them to wait for another vehicle. On all vehicles (including subway cars), it is disrespectful to stand near doors and block the exit, especially when it is not your stop.