Bumper Guardian

By Warren G. La Heist and Frank G. Ephraim, NHTSA Report Number DOT HS 807 072

Principal Findings

Damage to Safety Other Parts

• In unreported low-speed collisions, there is no statistically significant difference in the damage frequency of safety-related and other bumper protected parts in models equipped with changed bumpers compared to models with unchanged bumpers.
• The insurance data revealed that parts such as lamps, radiators, trunks and fuel tanks showed no significant change in damage frequency in cars protected by changed bumper systems. Only hood latches incurred a higher rate of damage in cars protected by changed bumper systems. Past-studies have shown that hood latches rarely malfunction and when hoods fly open, they seldom cause collisions.

Override and Underride

• The bumper standard modification did not change bumper height requirements. The difference in bumper contact frequency of 1983/1984 changed bumper systems (86 percent) and their 1981/1982 predecessors (83 percent) is not statistically significant.

Benefits and Costs

• Collision damage repair costs dropped for both changed and unchanged 1983/84 models, relative to their 1981/82 predecessors. The unchanged model repair costs dropped more, but the $36 difference between these and the changed systems is not statistically significant. The Final Regulatory Impact Analysis (FRIA) prepared in 1982 projected a $76 increase (in 1984 dollars) in lifetime collision damage repair cost for bumpers designed to meet the 2.5 mph standard.
• The lifetime cost of the combined front and rear bumpers of changed systems relative to unchanged systems dropped by $44. The FRIA in 1982 projected a bumper system cost reduction of $91 (in 1984 dollars) for bumpers designed to meet the 2.5 mph standard.
• The net benefit of changed versus unchanged systems is $8 ($44 decrease in bumper cost minus the $36 increase in lifetime collision damage repair), over the life of a car, but this change is not statistically significant. There still were no significant differences in net benefits between changed and unchanged bumper systems even when benefits and costs were disaggregated by facebar, structural, energy absorber and a combination of structural and energy absorber changes. The 1982 FRIA projected a $15 net benefit.

Time and Inconvenience

• The driver survey of low-speed, unreported collisions yielded estimates of the average time spent in connection with incidents involving damage, as follows:At the scene: 35 minutesFilling out forms: 78 minutesGetting repair estimates: 4 hoursGetting car repaired: 1.5 daysTime without use of car: 2 days

  There was no difference in the amount of time expended per incident between cars with changed bumpers compared to cars with unchanged bumpers. However, on a lifetime basis, given the respective collision damage rates of changed and unchanged cars, there is a net increase in cost of $4 for cars equipped with changed (reduced strength) bumpers.

Conclusions

• The costs to consumers have not changed as a result of the modification of the bumper standard from 5 to 2.5 mph.
• The net effect, over a car’s 10 year life, is a small increase in repair cost, which is offset by a reduction in the cost of the bumpers.
• The change in the bumper standard has not affected the protection of safety-related parts.

By Warren G. La Heist and Frank G. Ephraim, NHTSA Report Number DOT HS 807 072

Principal Findings

Bumper System Weights and Costs

• Combined front and rear bumper systems that were changed — that is reduced in strength — after the standard was modified, weighed less than their 1981 and 1982 model predecessors. The 1983 model bumpers weighed 72 lbs. compared to 85 lbs. for the 1981/82 models. In 1984, the average bumper that was changed, weighed 74 lbs.–a slight gain over 1983 models.
• Costs of bumpers decreased from $138 (1984 dollars) for the 1981/82 models to $114 for 1983 models. By 1984, bumper costs went back up to $125 because more energy-absorbing materials were added to certain bumper designs, and in some cases, aluminum was substituted for steel in facebars.
• In 1984 more than 50 percent of the new passenger car fleet was equipped with bumpers that incorporated a design change which reduced the strength of the bumper.
• The dominant design change was a reduction in the number of structural bumper parts such as reinforcements to facebars, brackets and end caps. In 1984, one quarter of the cars produced had bumpers with this change. They were 13 lbs. lighter and cost $21 less than their 1981/82 model predecessors.
• Another design change was the thinning of the main bumper strength member–the facebar. This was done on 14 percent of the 1984 passenger car fleet and resulted in a 6 lb. weight drop and a $7 cost reduction relative to 1981/1982 models.
• A combination of changes was made on 10 percent of the 1984 production fleet, including the replacement of hydraulic or similarly actuated plunger-type bumper energy absorbers with rigid brackets. Selected structural parts were also eliminated. The substitution of rigid brackets for hydraulic energy absorbers would normally result in a cost reduction and little or no change in weight, but due to the use of more costly high impact absorbing plastics instead of standard plastics for the fascia, prospective cost savings were offset to yield only a net reduction of $3. Weights of this group of bumper designs dropped by 7 lbs. due solely to the elimination of structural parts.
• In 2 percent of the 1984 production fleet, the only design change affecting energy management was the substitution of rigid brackets for hydraulic energy absorbers. This group also included the use of aluminum in place of steel for facebars or reinforcements. The added cost of this change in material offset most of the drop in costs for replacing the energy absorbers with brackets yielding a net reduction of $6. A substantial weight reduction of 18 lbs., relative to 1981/82 predecessor models, was due entirely to the material substitution.

Collision Damage Frequency

• The 1984 and combined 1983 and 1984 changed bumper models did not encounter a significantly different rate of damage frequency, compared to unchanged bumper models, in low-speed unreported collisions.
• Based on collisions for which an insurance claim was filed, there was an increase of 6 percentage points (from 59 to 65 percent) in the proportion of bumper-related damage claims for 1983/1984 changed bumper-equipped models. Most of the increase was attributable to claims for rear end damage. Beyond a fairly low impact speed, a bumper offers little or no protection. In frontal collisions, the bumper is less of a factor in preventing damage since these generally involve higher impact speeds than rear collisions. Therefore, increased damage is more likely when rear bumpers are built to a reduced standard.

Damage Repair Cost

• In unreported low-speed collisions, the average cost to repair damage is $450. There was no significant difference in damage repair cost between changed and unchanged 1983/1984 bumper models, relative to their 1981/1982 predecessors, when front and rear bumper systems are combined.
• Bumper-related damage that is severe enough for an insurance claim costs, on the average, $1,000 to repair. This average value is based upon reported incidents involving both changed and unchanged bumper systems for the whole range of 1981 through 1984 models. Repair costs of 1983/1984 changed models showed a statistically significant reduction of $62 when compared to their 1981/1982 predecessors.