Higher interest rates resulting from the credit crunch have made cars less affordable. That’s the conclusion of Comerica bank’s annual auto affordability study (pdf), which measures the cost of buying a new car in terms of how many months of the average American’s income an average new-car purchase would consume.

In the last quarter of 2008, that number was 22.8 months, up from 22.3 months in 2007, primarily due to higher interest rates, according to Comerica.

However, with more and more Americans unemployed, and no end to layoffs in sight, the two-week increase may not tell the whole story. Fewer Americans employed will reduce the average income, which seems like it should drive the affordability index up even more than interest rates in the future.

In any case, it seems no surprise that Americans are having more trouble (or at least delaying) buying new cars. Just ask all those who haven’t been showing up in dealerships in the last few months.

Still, auto affordability is an interesting statistic, and one that will bear watching as new fuel economy regulations and new safety features drive the cost of new cars up, and presses down on income levels. Going forward, something’s got to give.

—Eric Evarts

Also read: "Survey shows consumers are holding off on buying a new car."