As to why this matters, I've already noted that this is argument is a huge turn-off for those who drive older cars (just look at the comments section of any articles discussing the study). It's actually worse than that though: some families really are spending $9,000 or more per vehicle every year, but the type of person earning enough to buy a new car every five years is the last person you're going to convince to get rid of their car for economic reasons. For the most part, people who burn through cars that quickly are not hurting for money. The people who might actually be swayed by concerns about their transportation spending are exactly those for whom this number is least accurate.

Just to grind this point into the dirt, 15,000 miles a year is a lot of driving. If you drive that much, there's a good chance you live pretty far away from all you do: work, go to the movies, shop for groceries, visit friends, etc. The easiest and most likely car-to-transit convert is someone who lives closer-in, nearer to city centers where transit, bicycling, and walking access is much better. So again, if you want to focus on those people the 15,000 mile estimate (and associated costs) is probably way too high.

I've written about the impact of transportation costs on peoples' lives and think it's incredibly important that every car owner understands the true, full cost of driving. The way to do that, however, is not to offer a one-size-fits-all number, especially one that doesn't even fit anyone. If asked to calculate how much they spend on driving, including the cost of purchasing their car, maintenance, and all the rest, people are perfectly capable of doing so. The problem is that not enough people are being asked, or asking it of themselves.

Whatever the cost is for the individual, the question then is whether the freedom of movement they get from owning a car is worth that amount. Is that freedom worth $4,000 a year to you, even in light of the health, safety, and environmental benefits of more active forms of transportation (assuming those things matter to you)? How about $6,000? Even if $6k a year could buy you a home worth $100k+ more than your current one, or pay off your loan ten years early? These are questions that can really change a family's thinking on transportation. Starting off that discussion with what amounts to a lie can shut that conversation down before it's even begun, so we need to be careful when communicating costs to those who know them best.