Let's be clear PARK(ing) Day is not about being "anti-car" it's about being "pro- public space"
There is vast, vast array of literature about public space design and urban design. Let me share some of my heroes -
Jane Jacobs. She was an urban writer and activist who championed new, community-based approaches to planning. Best known for her 1961 book Life and Death of Great American Cities, her principles are still used and quoted today. She never was a urban planner and relied on her observations and common sense to illustrate why certain places work, and what can be done to improve those that do not. (I actually think PARK(ing) Day is very much in the spirit of Jane Jacobs - she proves that you don't need to be planner to care and get involved in city planning issues)
Jan Gehl. Known for public space research and books such as "Life Between buildlings", "Public Space- City Life" and "New City Spaces". This architect and urban designer is famously promoting the Copenhagen model across the world to cities including Melbourne, Sydney and New York. He established 14 questions/criteria about public space design focused on protection/safety, comfort and enjoyment.
Enrique Peñalosa. Former Lord Mayor of Bogota, and recent visitor to Brisbane, he transformed a city of seven million from a third-world gridlock of congested streets to a poster child for sustainable cities. He achieved this with a strong focus on public infrastructure such as public spaces, cycleways and public transport.
What is the commonality between them and other famous placemakers? I'd say a very strong value based in designing places for people.
'Urban public spaces are a means by which people can have contact with nature and with other human beings. A well designed public space encourages people to stop, sit down, and enjoy the trees, the birds, and the presence of other people. It should make people feel comfortable with each other, and encourage spontaneous conversation." (Urban Ecology Australia)
So design your PARK with people in mind, and think about what space YOU would want to visit?