Humanity comes to its senses and realises that the Earth is a finite size. The rich countries and even USA decides to consume less. Developing countries are careful not to make the same mistakes that the developed countries have. Oh yes, and pigs start flying. Journeys by car and plane increase.
Roads get more and more jammed and polluted.
The skies get fuller, and air and sound pollution becomes serious. Taxes and tolls mean that cars are increasingly only used by the wealthy. Good public transport encourages people to use it. The car becomes unfashionable, even shameful. People start changing their whole life, including where they live, or work, so they spend less time journeying to places, and even discover the joys of walking or bicycling.