Front and rear bumpers on today's cars generally consist of a plastic cover over a reinforcement bar made of steel, aluminum, fiberglass composite, or plastic. Some automakers design the bumper bar and its attachment brackets to crush in a low-speed crash to absorb energy. Polypropylene foam or plastic honeycomb, also called "eggcrate," sometimes is used in addition to or instead of crushable brackets and bar. But frequently this foam's main purpose is to serve as a spacer between the bar and the bumper cover and not as an energy absorber. A very few bumper bars are attached to the vehicle structure through mechanisms like shock absorbers.

A bumper reinforcement bar, shown without the plastic bumper cover

Bumpers are supposed to keep damage away from safety-related equipment such as headlights and taillights and protect vehicle parts such as hoods, fenders, and exhaust and cooling systems that are expensive to repair. When bumpers are poorly designed, these car body parts sustain most of the damage in parking-lot collisions and other low-speed impacts. Bills to fix fender-bender damage can add up to thousands of dollars fast, not to mention the hassle of getting repair estimates and waiting for your car to get out of the shop.

Insurance claims related to fender benders add up, too. This is reflected in the premiums consumers pay for auto insurance. More than $6 billion is paid out each year to cover claims of $4,500 or less, the kind of damage claims associated with low-speed collisions.¹ Such huge damage costs are why it's important to equip passenger vehicles with bumpers that effectively reduce damage in low-speed collisions. Better bumpers mean less out-of-pocket costs for consumers and lower insurance costs.

Geometry, stability, and energy absorption. Bumpers on colliding vehicles should line up geometrically so that they engage each other during a low-speed crash to absorb crash energy. The bumpers should overlap each other enough to account for variations in ride height and preimpact braking, which can lower the front end or raise the rear end of a vehicle just before impact. Bumpers should stay engaged with the other bumpers in collisions instead of overriding or underriding them, which often results in damage to vehicle grilles, headlights, hoods, fenders, and trunks. Bumpers also should have sufficient energy-absorbing capabilities to confine damage to the bumper system itself.²

Beyond these basic attributes, good bumpers extend to the corners of vehicles to protect headlamps and fenders.³ They're outset somewhat from the sheet metal parts they're intended to protect, leaving space for energy absorption. Bumpers also should be designed so they'll be relatively inexpensive to repair or replace after low-speed collisions.

The US government sets minimum bumper performance requirements for passenger cars,⁴ but these regulations don't apply to vans, SUVs, or pickups. The agency issued its first bumper standard for cars in 1971.

See NHTSA's bumper Q&A

Current bumper rules, in place since 1982, specify 10 bumper tests, including pendulum tests and crashes into a fixed flat barrier. The pendulum tests include 2 front and 2 rear corner impacts at 1.5 mph plus 2 front and 2 rear tests at 2.5 mph. The pendulum has a bumper-shaped protrusion that may impact the vehicles anywhere between 16 and 20 inches from the ground, and the mass of the pendulum equals that of the tested vehicle. Following these tests, the fronts and rears of the vehicles crash into a flat barrier at 2.5 mph. In these barrier and pendulum tests, unlimited damage is allowed to the bumper, but none is allowed to other parts of the vehicle. Hood and trunk doors must operate normally. Propulsion, suspension, steering, and braking systems also must operate normally. There can be no broken headlights or fuel, cooling, or exhaust leaks or constrictions.

Yes. The government tests are run at just 2.5 mph for full-width tests and 1.5 mph for corner impacts, and the result is too many inadequate bumpers. Bumpers used to do a better job of resisting damage in minor impacts. Under federal requirements that were in effect until 1982, car bumpers had to keep damage away from vehicle safety equipment and sheet metal parts in collisions at speeds up to 5 mph. Even allowable damage to the bumpers themselves was limited. Since 1982 the test speed under the standard has been cut in half, and unlimited damage is allowed to vehicles' bumper systems. Federal bumper rules also should extend to vans, SUVs, and pickups, and address the mismatch between car bumpers and those of these higher riding vehicles.

Even though the federal requirements for cars are weak, they do ensure that cars are equipped with bumper systems located at least partially in the test zone of 16-20 inches from the ground. Some vehicles that aren't subject to these requirements don't have any bumpers at all. Most pickups and SUVs do have bumpers, but their heights often vary from the federally specified test zone for cars. This means they don't interact with the bumpers on cars with which they collide. The energy of these collisions may go right past the bumpers and into the vehicle bodies, causing damage. Or the bumpers may engage but then slide off of each other instead of staying engaged. Either way the result is expensive car body damage.

Bumpers on cars and SUVs often don't match up in collisions

No. Automakers use a variety of designs to meet federal performance requirements for car bumpers. Some designs result in bumpers that don't protect expensive vehicle parts from damage in real-world low-speed collisions. The bumper covers on most modern cars fit snugly against the vehicle body. This stylish look doesn't help when it comes to resisting damage in low-speed collisions because there's not much room for absorbing crash energy before it reaches the car body and damages it. The emphasis on a sleek look encourages designers to shorten the width of the bumper bars that extend across the fronts and backs of vehicles, resulting in bumpers that don't do a good job of resisting damage.

The Institute has revamped the flat-barrier and pole bumper crash tests it has conducted since 1969. The 4 tests in the new series do a better job of reflecting real vehicle-to-vehicle collisions and the kinds and amounts of damage they cause. Instead of a flat barrier, the Institute now uses a test barrier that's shaped like a bumper on a real vehicle and has a deformable surface. The steel barrier's plastic absorber and flexible cover simulate typical cars' energy absorbers and plastic bumper covers. Vehicles strike this barrier in 4 tests — full-front and full-rear at 6 mph, plus front and rear corner impacts at 3 mph.

In the front and rear full-width crash tests the barrier is set 18 inches off the ground, and in the corner impacts the distance is 16 inches. These measurements are in keeping with federal rules that specify a zone for car bumpers 16 to 20 inches from the ground. The Institute's test barrier is 4 inches tall, or about the same as many real car bumpers. Results indicate not only the strength of car bumpers but also how well they engage, and then stay engaged with, the bumpers on other vehicles with which they collide. The test configurations produce the kinds and amounts of damage that commonly result from actual low-speed collisions.

IIHS bumper barrier tests

Not great. The bumpers often don't line up geometrically, and if they do engage they don't stay engaged during impact to absorb crash energy. Another problem is that the bumpers on many vehicles aren't wide enough to protect the corners. The first set of cars to undergo the new Institute tests showed that automakers still are using bad bumpers.

Midsize cars. In the full-front tests, only 4 of 17 midsize cars tested stayed engaged with the test barrier instead of going under or over it, and only one of these had damage limited to the bumper itself. The result was lower damage totals than other cars in the same test. Headlights, some expensive to replace, were damaged in every front corner test. Also, 13 of the vehicles required expensive repair to the sheet metal (fender), and the radiator support was damaged in 6 vehicles. Only one car's bumper bar was damaged by contact with the barrier itself; the others were too narrow to engage the barrier at all.

Results were similar in rear tests. Reducing the damage required the bumpers to engage the barrier and absorb the energy of the impacts, but this mostly didn't happen. Six of the 17 cars' bumpers slipped under the bumper barrier and sustained the most extensive damage. Only 3 had damage that was mostly confined to the bumper system. In the rear corner tests, only 3 cars had bumper bars wide enough to offer some protection to the rest of the car and keep most of the damage in the bumper system itself.

See Status Report, Vol. 42, No. 2

Midsize luxury cars. Midsize luxury cars did not perform any better. Only 3 of the 11 vehicles tested stayed engaged with the barrier in the full-front test, with only one vehicle limiting damage to the bumper itself. In the front corner test, headlamps were damaged on 9 vehicles, and fenders required repair on 6 vehicles. Again, only one of the vehicle's bumpers was damaged by direct contact with the barrier itself; the others were too narrow to engage the barrier at all. In the full-rear test, 7 of the 11 cars' bumpers slipped under the bumper barrier and sustained expensive damage. Only 2 vehicles had damage that was confined to the bumper system. Only 2 cars in the rear corner test had bumper bars wide enough to offer some protection to the rest of the vehicle and keep most of the damage in the bumper system itself.

See Status Report, Vol. 42, No. 8

Minivans. Minivans performed somewhat better than the midsize cars tested. This is in part because the minivans' front bumpers are about an inch higher off the ground than the car bumpers (about 17 inches compared with 16). The extra height reduced underride among the minivans and this, in turn, reduced damage in the full-front barrier tests. Four of the 6 minivans tested had headlamp damage and 2 needed fender replacement in the front corner test. The tailgates on 5 of the 6 minivans sustained damage in the full-rear barrier test. The minivans performed much better than the midsize cars on the rear corner test. This is because 5 of the minivans tested have stowable 3rd row seats that fold into the floor. This feature requires that the frame rails be wider to accommodate the storage space. Because the bumper systems attach to the ends of the rails, the bumpers also are wider and therefore do a better job of protecting the rear corners from damage in low-speed collisions.

See Status Report, Vol. 42, No. 11