Big cities often have problems that town and rural area do not have. Two of the biggest problems are heavy traffic and the pollution that cars create. Of course problems and pollution are not only found in big cities. However, the higher popylation and large number of vehicles on the roads in cities can make the problems happen more often with more noticeable effects. One of the most common traffic problems in big cities is congestinon. As the population of a city increases, and the number of vehicles on the road does,too. Cities can't always improve the size of their roads anf highways to keep up with thw number of vehicles. That results in traffic congestion, or traffic jams. When traffic jams happen, vehicles that are stuck in the congestion continue to run their enginne. This creates pollution and it is a big problem. Pollution causes problems for the people in cities and also hurts the environment. 1. Where do traffic problems and pollition usually happen? 2. What are causes of the problems? 3. When traffic jams happen, why do they cause pollution? 4. Does pollution cause health problems?