If two cars crash they can hurt the people inside or around them. Traffic Jams happen when there are too many cars trying to go the same way. They can create pollution if too many are used in a small area like a city.

Many places with many people have public transportation - buses, trains, and subways - that can help many people get to different places very quickly. Carpooling is putting more people in one car to use less fuel and create less pollution.