text: Limiting the use of cars could help reduce the amount of pollutants in our environment.  In Source two, it states, "Cold nights and warm air caused the warmer layer of air to trap car emission."  This tells us that car emissions are being caught in the air due to the weather, causing a layer of smog to settle over congested cities.  By limiting the use of automobiles, the layer of smog was able to vanish, but if we were able to limit cars permanently, then we would not have to worry about it in the first place.  In Source four, it tells us that, "If the pattern persists... it will have beneficial implications for carbon emissions and the environment, since transportation is the second largest source of America's emissions."  This proves that car emissions are harmful to the environment and that future generations are at risk because of the pollution already in the air.  Also, the statement shows that Americans are very dependant on transportation, but are unwilling to try a different method such as walking and biking.  By reducing the number of cars on the road, our environment would be helped tremendously.