Public transportation in North America varies greatly from place to place. Some large cities like New York, Boston, Toronto and Montreal have subway systems. These same cities usually also have train service into the city. But most towns and cities do not have subways or trains. Some do not even have buses. Most big cities have some sort of public bus service. In most North American cities, people who use the buses complain about poor service. This is partly because most people prefer to drive a car. Automobile companies spend billions of dollars on advertising. They want to convince young people that they should drive a car as soon as they are old enough. Even when public transportation is very good, most North Americans prefer to drive cars. So mostly students, poor people and seniors use buses. The large car companies have a lot of economic and political power in North America. They can usually convince politicians to limit the money put into public transit. Lobbying by large car companies has been effective in closing down many railway lines. In some cases, large corporations have bought train tracks, and torn them up so that no one could use them again. Because of this, nearly all transportation in North America is by car, bus or truck. The automobile created the modern North American city. Cars allowed families to live outside the city and drive back in to work. Since the 1920s, large numbers of Americans have lived in the suburbs, and used cars to do nearly all their daily activities. People drive to school, to work, to the shopping mall, to the theatre, to church and to doctors, lawyers and dentists. Because the modern city is so spread out, it is difficult to get where you want to go by walking, or even by bicycling. But the automobile also causes problems. Car accidents are a major cause of death and injury. Crowded streets and snarled traffic can lead to road rage. Frustrated drivers sometimes get out of their cars to fight each other. Young people often use cars as super toys. They enjoy driving very fast and take risks while driving. A high proportion of serious accidents concern drivers using alcohol or drugs. More recently, some people have accused cell phones of being a cause of accidents. About half of the air pollution in North American cities is caused by motor vehicles. The exhaust fumes from cars and trucks are part of this. The other part is that vehicles erode the surface of the highways. Small particles are torn loose from the road and thrown into the air as cars whiz by. Heavy trucks are particularly large contributors to particle pollution. Especially in hot weather, a layer of smog covers many cities. Much of this is caused by motor vehicles. Because city roads are often crowded, the result is frequent traffic jams. When cars are moving very slowly, bumper to bumper, it adds to air pollution. Another problem with cars is that not everyone can afford one. The average car costs nearly $20,000 to buy, and about $4,000 a year to operate. So cars are also a status symbol. People with cars tend to move out of the city. As a result, downtown areas are usually where the poorer people live. For a long time, many people have said that governments should try to make downtown areas more attractive to live in. This would include improving public transit, into and inside, the cities. Then some people may move back from the suburbs. And air pollution levels will decline. Right now, the large automobile companies and oil companies oppose these measures. Recently, there have been cuts to public transit in many cities. Whether these cuts continue, or whether they get reversed, is a big political issue in North America today.