Don't expect to have extra legroom when using public transit, especially during rush hours. It doesn't matter what type of public transit you use, in many cities, it can be guaranteed that you will have a lot of fellow passengers. For subways and buses, this might mean being forced to stand. Carrying items such as groceries can also be nearly impossible on some types of transportation, limiting your options to private cars or taxis.
Except for taxis, most modes of public transit have specific routes that may not be conveniently located. If you are running late and you intend to get to your destination quickly, opting for public transit like a bus or a train may not be the answer. Most routes are, of course, designed to follow paths used by largest number of people. In some major cities, buses and trains only have stations on main roads and highways.
Public buses and trains often run on a schedule, so passengers have to be at the station by a certain time. If passengers miss their bus or train, they may have to wait for up to an hour before the next one comes. If you are running late and have some extra cash, it's better to call a taxi to avoid waiting. Another disadvantage is waiting for disabled trains or buses to get going again. All of the above scenarios make spontaneous travel much trickier than driving.
Don't be surprised to board a bus or train that's dirty. Although the management running public transportation services probably has a cleanup system in place, after hundreds or even thousands of people use something on a given day, litter and general surface dirt will quickly add up. Safety can also be a concern on crowded public transit systems, which often offer a playground for pickpockets and other petty thieves.
