One thing that must be discussed is growth - both in population and in geographic size.
As we increase our population, the number of cars on the road increases, and our traffic gets worse. Yes, we can add lanes to the road, but that make somethings worse. For example, it is harder to make a left turn onto a larger road or for a pedestrian to cross a larger road.
As we take more land, we destroy more woods and farmland, converting forests and farms into subdivisions.