An insurance group is raising concerns about minivan bumpers, contending that weak federal standards permit automakers to build cars that suffer thousands of dollars in collision damage even in impacts at walking speed.The Insurance Institute for Highway Safety, based in Arlington, Va., says the worst performer among six 2008 minivans it recently subjected to four low-speed crash tests was the Nissan Quest, with resulting damage that would have cost more than $8,000 to repair. "It's damage that consumers shouldn't have to pay for, or put up with the aggravation of having to get their vehicles repaired," institute senior vice president Joe Nolan said in a statement.The tests are conducted at either 3 mph or 6 mph to simulate typical mishaps in heavy traffic or parking lots. Vehicles are bumped into a flexible barrier mimicking the design of a car bumper.Nissan noted in a statement that bumper strength is an issue of cost, not safety. The automaker said, "We will study and analyze the test results to help understand how we can keep insurance premiums low for our customers."The best performer in the group was the Honda Odyssey, the institute said, but its damage still totaled $5,258. Federal government bumper standards are "very weak" the institute said, requiring only that bumpers resist damage to safety gear like headlights in a 2.5 mph impact. And the rules apply only to cars, not minivans or sport utility vehicles. Other vehicles tested and their total damages were the Dodge Grand Caravan, $5,495; Toyota Sienna, $5,726; Chevrolet Uplander, $5,799; and Kia Sedona, $6,525.