We found our cat chestnut hiding under a car in a busy street.
That's crazy. Why does the cat hide under cars?
There's some cars that scare cats. There's one time I was petting my cat and it ran away because of a car.
This is why I do not trust taking the cats outdoors. They can run away so easily and it is scary if you cannot find them.
I tried using a leash but cats are unreactive to different methods of training.
Maybe your cat should just spend its time inside where it's safe and nothing can harm it.