City traffic is a great problem. More cars are produced every year and the streets are getting more and more crowded. So during rush hours when people are going to or from their work, traffic is brought to a standstill. It has been suggested that commuters (people who travel to work every day from outside the city) should share their cars and give each other lifts. So each car would carry four or five people instead of only one. It is an excellent idea; however, so far nobody has been able to think of a way to compel people to do so.