Air pollution
Highway congestion
Air pollution has caused it because the engine of the cars has made the smell of the air be not very nice, and people could end up being ill because of having to breathe in petrol, because they might have an allergen.
Highway congestion because there are so many cars these days, that most of the time you go on a highway (motorway), there are loads of cars queueing. This can also cause air pollution because the animals that might be in a field at the side of the motorway won't like the smell of all those cars.
