  Place a car independently with probability $p$ at each site of a graph. Each
initially vacant site is a parking spot that can fit one car. Cars
simultaneously perform independent random walks. When a car encounters an
available parking spot it parks there. Other cars can still drive over the
site, but cannot park there. For a large class of transitive and unimodular
graphs, we show that the root is almost surely visited infinitely many times
when $p \geq 1/2$, and only finitely many times otherwise.
