In my experience suburbs and rural areas are even worse for public bathroom access (and even delivery of most other public goods except education). Are there US suburbs with plentiful public bathrooms?
What's a suburb? Depending on the level of density and sentiment about public parks (poor people's lawns v. a public good), some relatively low density places are better about public bathrooms. Boise is something like 5K people per sq. mile downtown, but there's public bathrooms at regular intervals on the Greenbelt in places at lower 3K densities.
As homelessness has gotten worse though, there's been noticeable encampments/vehicle caravans building up at these bathrooms.
As homelessness has gotten worse though, there's been noticeable encampments/vehicle caravans building up at these bathrooms.