There is also data online which shows how commute times are increasing for people. For instance, between 1990 and 2000 there was a 50% increase in the number of people who commuted more than 60 minutes to their job.
Stressed city infrastructure, water restrictions, overcrowded public schools, skyrocketing property taxes, are all related to increased population use of the social infrastructure. City boundaries extending into wildlife areas, increased forest fire risk to homes .
When you have a stable social foundation and you add more people to that foundation, the new additions have to be positive economic contributors in order to keep the systems functioning as they are or improving them via more funding. When the newcomers are not carrying their weight, then they have to be subsidized and that reduces the quality of the public sphere.
What exactly do you see as trigger points for there being too many people in the US? How about sprinkler bans for outdoor watering? They used to be unheard of in non-desert areas 40 years ago.