There isn't enough room for them, so all the cars have to go very slowly. Some people don't think that this is the cars' fault. Whenever a new freeway opens or a popular road is widened, people usually take more trips and do more driving. In a lot of places there just isn't any more room for new roads, even if the government wanted to build them. In Los Angeles, for instance, most of the freeways were built between 1950 and 1970, when four to six million people lived in the county.
Some people try to get away from traffic jams by moving to the suburbs.
A suburb is a community that's close to a city, but not really part of it. The adults can go into the city to their jobs, but live in a place that feels more like a small town. Suburbs start when the government gives permission for homes to be built on undeveloped land. Roads are put in, and water, sewage and electric lines. Supermarkets, hardware stores and other businesses move in to sell things to the people who buy the new homes.