today, most people in the city rely on automobiles as a means of transportation. while many people still take the city buses, more and more are driving to work every in their own cars. to many city dwellers, cars have become a necessity. but too many cars in the street also create problems. traffic congestions, accidents and air pollution are the three most obvious problems that accompany a sharp increase of cars. we often get caught in heavy traffic during the rush hours, when it takes a long time to move forward even an inch. and thousands of people die while a greater number are injured, some crippled for life,