According to a 2009 study by the Insurance Institute for Highway Safety (IIHS), the design of most current midsize cars results in extremely high repair bills, and therefore large penalty increases in car insurance premiums, even for low-impact road accidents (or “fender-benders”).

Of the six most popular midsized sedans (the Honda Accord, Hyundai Sonata, Mazda 6, Nissan Maxima, Ford Fusion, and Chevrolet Malibu), none earned the top rating of “good” in extensive tests performed by the IIHS. “Consumers buy midsize cars for practical reasons,” said Joe Nolan, Senior Vice President of the IIHS. “There’s nothing practical about a $1,000-plus repair bill after a minor bump in commuter traffic.”

The Institute has developed a new rating protocol for bumpers, assisted by two rounds of tests. The protocol takes into consideration real-world damage patterns, average repair costs, and the frequency of insurance claims. Vehicles were tested for impact at 3 and 6 mph and then given a rating of good, acceptable, marginal, or poor based on what it would cost to repair the entire front bumper; the entire rear bumper; just the corner of the front; and just the corner of the rear.

The best-performing vehicle, the Mazda 6, averaged a repair cost of $871 and was given an “acceptable” rating. The only other current vehicles rated acceptable are the Ford Focus, Smart Fortwo, and Scion xB. “Although midsize car bumpers still allow way too much damage in minor impacts, it’s encouraging that some manufacturers are designing better ones,” says Nolan.

The worst performing vehicle, the Chevy Malibu, averaged a repair cost of $2,329. The Ford Fusion also received a “poor” rating, with an average repair cost of $2,207.

“Ford fit the Fusion’s front and rear with weaker bumper beams, and this had a big effect on the test performance,” said Nolan. The Malibu repair bill is high in part because the front grille actually protrudes past the center of the bumper; as a result, the grille and Chevy emblem are destroyed on impact. Those parts alone cost more than $600 to replace.

U.S. federal regulation of bumper strength is minimal. Canadian standards were higher until last year, which meant that automakers that sold the same vehicles in the U.S. and Canada had to manufacture the vehicles to Canadian standards, which required bumpers to prevent damage to headlights at impacts up to 5 mph. The new lowered standard is 2.5 mph for full front and rear bumpers and only 1.5 mph for all corners.

The amount of repair bills can dramatically affect a driver’s car insurance rate, making the issue of great interest to the IIHS, especially in an economic environment in which many drivers are foregoing car insurance because they can’t afford car insurance rates and are willing to risk having to pay repair bills themselves. It is estimated that if the current trend continues, 1 in 6 drivers will be uninsured by 2010.