Bumpers, even those on expensive cars, don’t resist damage in low-speed impacts. The Infiniti G35, the worst performer, sustained almost $14,000 damage in a series of four tests conducted at 3 and 6 mph by the Insurance Institute for Highway Safety. The Saab 9-3 was the best, sustaining $5,243 damage. Only three cars sustained less than $6,000 damage, while four would cost more than $10,000 to fix.

        “The Infiniti was a disaster, and even the Saab sustained way too much damage in these low-speed impacts,” said Institute senior vice president Joe Nolan. “There shouldn’t be much or any damage in collisions at these speeds, especially to expensive and presumably well-made cars.”

Why bumpers don’t bump

The purpose of a bumper is to absorb the energy of a low-speed collision before it damages expensive-to-repair parts like fenders and hoods. But there are multiple problems, the first of which is that the bumpers on colliding vehicles often don’t line up vertically so they don’t engage to begin with. Even some that do line up don’t stay engaged during an impact. Their aerodynamic styling may allow them to slide under the bumpers of the vehicles they strike. This means they can’t do the job of energy absorption.

        Another problem is that the bars underneath bumper covers, which are supposed to do the main work of absorbing crash energy, often aren’t up to it. They may not be big enough to provide much protection from damage, especially if they don’t extend to vehicle corners, or they may be too flimsy to absorb much energy.

        Something else driving high repair costs after minor bumps is the price of replacement parts to fix the damage. This is especially true of luxury cars, which are expensive not only to purchase but also to repair.

        To assess and compare bumper performance in low-speed impacts, the Institute conducts a series of four low-speed tests — full front and rear into a barrier designed to mimic the front or back bumper on another vehicle plus front and rear corner impacts. The full-width impacts are conducted at 6 mph while the more demanding corner impacts are run at 3 mph.

        These tests replace the 5 mph flat-barrier and pole tests the Institute conducted for decades to assess bumper performance. The new tests, which reflect years of development, more closely replicate the damage patterns in today’s low-speed collisions between vehicles. The first set of results of the Institute’s new tests involved inexpensive and moderately priced mid-size cars, which sustained up to about $9,000 damage in the four tests.

        “Luxury cars don’t perform any better than cheaper cars,” Nolan pointed out. “There’s nothing luxurious about shelling out thousands of dollars to fix damage from a bump at a speed no faster than a brisk walk.”

Make bumpers wider and taller

To do an effective job of managing crash energy, the bars underneath bumper covers have to be long enough to protect car bodies out to the front and rear corners. If a bar doesn’t extend far enough, a minor corner impact is likely to cause lots of damage, even compromising lights and other safety-related parts. The headlight on one car the Institute recently tested was damaged so much that it wouldn’t illuminate, and those on another seven sustained lesser damage.

        Bumpers also have to be tall enough to engage, and to stay engaged with, the bumpers on other vehicles in collisions, even during emergency braking. Otherwise the bumpers bypass each other when the vehicles collide, overriding and underriding so that crash energy goes right through and crumples the vehicle body.

        The Mercedes C class is a good example. Its front bumper is mounted so low that it underrode the barrier in the Institute’s front full-width test, escaping virtually unscathed. A little touch-up paint was all that was needed to repair the plastic bumper cover. What absorbed the energy of the impact was the C class’s grille, hood, radiator, headlight, and air conditioning condenser, all of which were damaged. This is how the repair costs escalated to more than $5,000, the highest total sustained by any of the 11 cars in any single test.

        “This is exactly what we don’t want to see,” Nolan said. “The car body took the hit.”

        On the other hand, the front bumper system on the C class includes a longer bar than on the other luxury cars. This reduced damage in the corner impact to less than $1,000, second best behind the Volvo S60's $543.