The question is if families are getting smaller because parents don’t want more kids or because of regulation[0]. Maybe requiring people to have smaller cars or use public transport would further cut the birth rate.

I’m only half-serious. I know there is good reason for public transport or having smaller cars in urban environments.

0: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3665046

Generally the deciding factor has been birth control. The more birth control is available and accepted as a choice, the more women choose to postpone their first child, which automatically leads to having fewer children.

> Maybe requiring people to have smaller cars or use public transport would further cut the birth rate.

This should be easy enough to test by comparing against cohorts in Europe and Asia.

Fertility rates plummeting is not necessarily a good thing in the long run, so maybe having kids should be incentivized.