The purchase of an average-priced new vehicle in the United States took 24.6 weeks of median family income in the second quarter, according to the auto affordability index compiled regularly by Comerica Bank.

The latest figure is down 0.1 week from the first quarter, and down 1.1 weeks compared to a year ago.

Including finance charges, the total cost of buying an average-priced light vehicle was $US28,479 in the second quarter, essentially unchanged from the previous quarter or a year earlier. Comerica estimated that median family income has increased 4.2% year on year.

"The cost of buying and financing a new light vehicle did not change much in the second quarter," said Comerica Bank chief economist Dana Johnson.

"The average amount spent on a new vehicle fell $50 in the second quarter after dropping $450 in the first.  The average financing rate for a car loan edged up 8 basis points to 4.86%. With gasoline prices high and house prices weak, the typical consumer continued to opt for relatively affordable cars and light trucks last quarter."