Large cities have massive problems with congestion. From the 1950s, car ownership has grown at a very quick rate. For example:
In 1975, a number of motorway roads ran through the heart of Belfast. However, these became over-crowded. So, a number of road developments were introduced to reduce congestion.
Both projects resulted in delays and diversions and when the roads were opened the congestion was as bad as ever.
This has meant that the journey time from one place in the city to another has increased considerably.
The longer cars are sitting in traffic jams, the bigger the impact on air pollution caused by the engines.
Vehicle exhausts can have negative effects on people who live in urban areas and on the environment.