There are lots of things you could talk about here. Try to sit down and make a plan based around the following ideas:
Cars have an environmental impact, they are extremely damaging due to the fumes that they give off. This can have subsequent effects on nature and humans alike.
Cars cost taxpayers money because of the need to renew and build roads. If less cars use the roads then one can presume there would less damage to repair and indeed less roads required for society as a whole.
Cars can cause health problems if people breathe in noxious exhaust fumes. Thousands of people die every year due to air pollution. Cars and traffic have a massive impact on the air that we breathe every day.
Cars can be very dangerous and cause deaths every year. Car accidents account for a large number of fatalities around the world. Limiting car use would presumably lead to less deaths and less injuries to humans everywhere.
