Some number of cars are always going to need to be made new in a year -- due to collisions, wear and tear, etc. It is better for everybody, ceterus parabus, if

Some number of cars are always going to need to be made new in a year -- due to collisions, wear and tear, etc. It is better for everybody, ceterus parabus, if newer cars are better at fuel efficiency and emissions. It is possible that the number of new cars is higher than it needs to be, but I am unaware of any evidence that suggests it is. Regardless, for each marginal car bought, it's better if that car is more fuel-efficient.