Just to clarify, there is no law that I know of prohibiting car traffic on yom kippur in Tel Aviv. However, since this is the most important holiday of the year, even many Israelis who don't celebrate other holidays will celebrate this one. I believe that virtually all businesses are closed that day, even those that don't close on other Jewish holidays (again, not illegal to operate, but customary). So in practice, few people will be driving that day/night.
Moral code or just social pressure - the discomfort of the thought of disobeying the tradition and everyone glaring at you as you drive down the road outweighs the benefits of doing so even if you don't believe in the tradition.
