A lot of times they're prettier, cleaner and quieter than most cities. And there's less traffic. More homes and roads are built, and more people move in, and more stores open to sell them things. Now all the new people are driving on the brand new roads, and on the roads of the first suburb, and on the roads of the city that the suburbs are built around. This is called sprawl .
Sprawl is one of the reasons there are so many traffic jams.
Most of the new suburbs aren't built for public transportation. People who live there need cars to get around. The government says that traffic in Los Angeles will get twice as bad by 2015, if things don't change. Right now only eight percent of the world's people own cars. Cars are used mostly in the richer countries.