The Great Recession will hopefully stop eventually, and then you can expect to see the unemployed 18-35 year-olds get jobs, buy cars (among other things), and drive again.
Data has shown that between 55+ retiring and younger potential drivers preferring not to drive, vehicle sales have plateaued. If self-driving cars take off in the next ~5 years, that'll be the death of a large part of the auto industry.
End result - car sales stagnate.