I've never personally owned a car, but I did grow up in a pretty car-centric area and am generally aware of my parents' purchasing decisions, in an environment where there wasn't a lot of money to go around.
If you must have a new car (we bought used fairly often, with good results), there are a dozen cars you can buy for around $15k, which works out to $270/mo with a 3.1% loan. I'm really stacking the deck here: I ignored cars that are too small, since I assume a family with children, I'm using a pretty high interest rate, and I'm ignoring used cars. Bear in mind that the _average_ payment means that it's ignoring the substantial amount of people who don't have kids and would be fine with a smaller car, or those with better credit who can get a better rate.
That being said, I don't know enough about the distribution of the discussed figure to say whether it makes sense in the way we're using it: $500 is the mean payment, not the median, so it would be a mistake to assume that there's an "average person" who pays $500. It's just as likely that some people have higher payments (that they can afford easily) and poorer people have lower ones.