ARLINGTON, VA --- Bumpers on 2009 models of the Honda Accord, Hyundai Sonata, Mazda 6 and Nissan Maxima performed better than their 2007 predecessors in low-speed crash tests conducted by the Insurance Institute for Highway Safety, the institute said. 

Bumpers on the 2009 Chevrolet Malibu and 2010 Ford Fusion, however, slipped in performance compared to earlier models, according to the institute. None of the six popular midsize sedans earned the top rating of "good" in a recent series of tests designed to assess and compare how well bumpers resist damage in everyday fender-benders. 

The Mazda 6 improved to "acceptable" from "marginal," with an average repair cost of less than $900 after four tests at 3 and 6 mph. The Accord and Sonata improved to "marginal" from "poor." The Fusion slipped to "poor" from "marginal," and the Maxima and Malibu remained "poor," the IIHS said. 

The Mazda 6 is only the fourth car tested under the new protocol to earn an "acceptable" rating for its bumpers. The others are the Ford Focus, Scion xB and Smart Fortwo. 

"Consumers buy midsize cars for practical reasons. There's nothing practical about a $1,000-plus repair bill after a minor bump in commuter traffic," said Joe Nolan, institute senior vice president. 

This is the second group of vehicles the institute has evaluated under a new bumper ratings protocol based on repair costs averaged and weighted to reflect real-world damage patterns and insurance claims frequency. The institute rates bumpers "good," "acceptable," "marginal," or "poor," based on performance in four tests -- front and rear full-width impacts at 6 mph and front and rear corner impacts at 3 mph. Each vehicle is run into a steel barrier designed to mimic the design of a car bumper, with the barrier's plastic absorber and flexible cover simulating typical cars' energy absorbers and plastic bumper covers. These tests are designed to drive bumper improvements that lead to better damage resistance in a range of real-world crashes, IIHS said. 

"Although midsize car bumpers still allow way too much damage in minor impacts, it's encouraging that some manufacturers are designing better ones," Nolan said. He pointed out that the front and rear bumpers of the 2009 Mazda 6 are wider, taller and higher off the ground than the 2007 model. 

Mazda, Honda, Nissan and Hyundai improved the bumpers on their 2009 midsize cars so the bumpers would better resist front underride, which exacerbates collision damage. Bumpers have to be tall enough to engage, and to stay engaged, with the bumpers on other vehicles in collisions, even during emergency braking, or they'll bypass each other when the vehicles collide. Preventing override and underride means crash energy is absorbed by bumpers instead of pricey vehicle parts such as hoods, grilles and fenders, or safety gear such as headlights and taillights, IIHS said. 

For more details, visit www.iihs.org.