People like cars for many reasons. Drivers don't need to wait for trains or buses to pick them up. Riders always have a seat, and don't need to sit next to anyone they don't like (except maybe their little brothers).

     Car owners can live far away from the city, on twisty streets in little towns that buses and trains don't go to. The houses in the little towns might be nicer and cost less than homes close to a transit stop.

     Car owners can drive into the mountains or the desert, anytime they want to. The roads are always open. They can go shopping and take home lots of things in their cars, and they don't have to wait for the bus in the rain.   >>

     In some places, drivers can travel two or three times as fast as people in trains and buses.

     Many adults are very busy. Some make many stops in their cars every day, to run errands or to pick up kids like you after school. It might be very hard for them to stop driving, if they live in places without good transit.

     But the trouble is, the popularity of cars is the main reason they cause so much trouble.

     There are too many of them!

     One of the biggest problems cars cause is air pollution.

     An internal combustion engine uses fuel by mixing it with air and then burning it. When this happens, some exhaust gases are always left over. The exhaust gases go out the tailpipe and into the air.   >>

     This isn't a problem if only a few people in a city drive cars; there's a lot of air! But what if millions of people are driving at the same time?

     The answer is smog. Smog is what happens when the exhaust gases mix with sunlight. Sometimes you can see smog as a murky brown haze on the horizon. But smog is bad for you even if you can't see it.

     In Los Angeles, smog got so bad that the government declared "smog alerts." A "smog alert" happens when the air is unhealthy to breathe. Sometimes kids weren't even supposed to go outside to play. People complained that the smog made their eyes water, and that they couldn't see well enough to drive.

     The smog made some people sick. Smog is especially bad for people who have problems with their lungs. Smog is one of the reasons that kids get asthma.

     But more and more people drove, and the smog got worse and worse.   >>

     Finally, the government passed laws that said that cars couldn't make as much pollution.

     The car makers put special controls on the new cars, so they wouldn't make as much smog. The oil companies changed the gasoline so it would burn more cleanly.

     Today a new car makes much less pollution than an old car. You'd need more than ten new cars to make as much smog as one 1968 Chevelle.

     The air in Los Angeles and some other cities is much cleaner than it used to be.

     In the 1970s, the government had to declare a smog alert in Los Angeles on almost every hot day. In 1998 there were only twelve smog alerts all year!

     But smog is still a serious problem. It can hurt kids' lungs and cause heart attacks in adults. Los Angeles still has some of the smoggiest air in the country.   >>

     Another big problem partly caused by cars is global warming. The burning of fuel in all cars, even new ones that don't pollute very much, puts a gas called carbon dioxide in the air.

     Carbon dioxide isn't pollution. Plants use it for photosynthesis. But the millions of cars, trucks, buses, factories and powerplants running all over the world are making much more carbon dioxide than would be in the air normally.

     The extra carbon dioxide helps trap the sun's heat on earth. The whole planet is heating up because of it.

     A few scientists say that global warming isn't a big problem. But most think it's very serious.

     Global warming may cause shortages of food and water in some places. It may make the polar icecaps melt, and the sea level rise. One study said that average temperatures could be as much as eleven degrees higher by the end of the century.

     No one really knows how the world will change if people make it hotter.   >>

     Cars use up a lot of space.

     In some cities, up to thirty percent of the land is taken up just by parking! Cars use freeways for fast driving, regular roads for slower driving, parking lots and parking garages. In a typical city, every car has an average of eight parking spaces.

     The next time you walk to school, look around your neighborhood at all the space cars use.

     I'll bet it's a lot!

     One reason kids in some cities don't ride bikes very much is that there are so many cars.

     Parents worry that the cars will hit their kids.   >>

     Just between 1975 and 1990, the total number of miles that Americans drove their vehicles increased by over fifty percent! What will happen if people keep driving more and more?

     The government says that traffic in Los Angeles will get twice as bad by 2015, if things don't change. But the city of Los Angeles alone already has more cars than the poorest sixty percent of the people in the entire world!

     And what will happen when all the people in the poor countries can afford cars too?

     Now only eight percent of the world's people own cars. Cars are used mostly in the richer countries.

     If there were 750 cars for every 1,000 people, as there are in the United States, there would be four and a half billion cars on the earth, all taking up space and making pollution.

     And the world's population is going to get a lot higher!

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