None of the six most-popular midsize sedans earned a top rating in bumper safety in the latest crash tests performed by the Insurance Institute for Highway Safety.

The Mazda 6 was the only car to receive an "acceptable" rating — one rating below "good," the top rating — based on the average cost to repair front, rear and corner bumpers following a 6 mph crash.

A 6 mph crash can simulate a common parking accident, such as backing into another vehicle. IIHS rates vehicles on a four-notch scale ranging from "good" to "poor."

The average cost for bumper repairs on the Mazda 6 is $871, according to IIHS. That's an improvement from the 2007 model which received a "marginal" rating. Mazda improved its bumpers by making them wider, taller and higher off the ground, IIHS said.

Ratings for the Honda Accord and Hyundai Sonata improved one notch to "marginal" from "poor," with the average cost of repairs coming in at $1,133 and $1,265, respectively.

"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 IIHS Senior Vice President Joe Nolan.

The 2009 Ford Fusion's bumper rating slipped to "poor" from "marginal" in 2007, with the average cost of repair reaching $2,207. Nolan said the car's weaker bumper beams had a big impact on performance.

"The Fusion's bumper buckled, which caused it to underride the test barrier, resulting in twice as much damage as the 2007 model in the rear test," he said.

"We are surprised by the results as Ford continues to lead the industry in cost-of-ownership by nearly any measure because we design our vehicles to help reduce operating and repair costs," said Wes Sherwood, Ford's safety communications manager, in a statement. He said the Fusion is the only car in its segment to offer Cross Traffic Alert radar technology that helps drivers avoid fender-benders in crowded parking lots where many of these accidents occur.

General Motors' Chevrolet Malibu also received a "poor" ranking, with average report costs hitting $2,329.

The average cost of repairs is weighted based on repair costs to the vehicle's various bumpers and real-world damage patterns. The full front and rear test results are given double the weight, IIHS said, because crashes that damage those bumpers happen twice as often as corner impacts.

Repair costs vary by vehicle depending on the complexity of the repair or extent of the damage. Part of the cost related to repairing the Malibu, for example, goes to replacing the grille, emblem, and decorative chromed plastic trim following a crash involving the front bumper, IIHS said.

"While the IIHS bumper performance rating may be of interest to consumers, it is important to note the rating does not reflect a vehicle's safety performance," said Janine Fruehan, manager of quality and safety communications for the automaker. "GM's focus is on occupant protection and crash avoidance."

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