A bumper is a structure attached or integrated to the front and rear of an automobile to absorb impact in a minor collision, ideally protecting occupants and minimizing repair costs. Invented by Briton Frederick Simms in 1901, bumpers ideally minimize height mismatches between vehicles and protect pedestrians from injury. Rigid bumpers transmit impact forces both to vehicle occupants and pedestrians; hence numerous regulatory measures have been enacted to reduce the risk to both, at the expense, however, of increasing vehicle repair costs.
- 1 Construction
- 2 Physics
- 3 Pedestrian safety
- 4 Height mismatches
- 5 Regulation
- 6 See also
- 7 References
- 8 Further reading
Bumpers were at first just rigid metal bars. On the 1968 Pontiac GTO, General Motors brought forth an "Endura" body-colored plastic front bumper designed to absorb low-speed impact without permanent deformation. It appeared in a television commercial where John DeLorean hit the new car with a sledgehammer and no damage resulted. Similar elastomeric bumpers were available on the front and rear of the 1970-'71 Plymouth Barracuda, and in 1971, Renault introduced a plastic bumper (sheet moulding compound) on the Renault 5.
Current design practice is for the bumper structure on modern automobiles to consist of a plastic cover over a reinforcement bar made of steel, aluminum, fiberglass composite, or plastic. Bumpers of most modern automobiles have been made of a combination of polycarbonate (PC) and Acrylonitrile butadiene styrene (ABS) called PC/ABS.
Bumpers offer protection to other vehicle components by dissipating the kinetic energy generated by an impact. This energy is a function of vehicle mass and velocity squared. The kinetic energy is equal to 1/2 the product of the mass and the square of the speed. In formula form:
A bumper that protects vehicle components from damage at 5 miles per hour must be four times stronger than a bumper that protects at 2.5 miles per hour, with the collision energy dissipation concentrated at the extreme front and rear of the vehicle. Until 1959, such rigidity was seen as beneficial to occupant safety among automotive engineers. Modern theories of vehicle crashworthiness point in the opposite direction, towards vehicles that crumple progressively. A completely rigid vehicle might have excellent bumper protection for vehicle components, but would offer poor occupant safety.
Bumpers are increasingly being designed to mitigate injury to pedestrians struck by cars, such as through the use of bumper covers made of flexible materials. Front bumpers, especially, have been lowered and made of softer materials, such as foams and crushable plastics, to reduce the severity of impact on legs.
The height and placement of bumpers may be[vague] legally specified, to ensure that when vehicles of different heights are in an accident, the smaller vehicle will not slide under the larger vehicle.
Bumpers cannot fully protect against moderate or high speed collisions, but their height from the roadway surface is important in engaging other protective systems. Energy-absorbing crush zones are completely ineffective if they are physically bypassed; an extreme example of this occurs when the elevated platform of a tractor-trailer completely misses the front bumper of a passenger car, and first contact is with the glass windshield of the passenger compartment. Airbag deployment sensors typically do not trigger until contact with an obstruction, and it is important that front bumpers be the first parts of a vehicle to make contact in the event of a frontal collision, to leave sufficient time to inflate the protective cushions.
Truck vs. car
Underride collisions, in which a smaller vehicle such as a passenger sedan slides under a larger vehicle such as a tractor-trailer often result in severe injuries or fatalities. The platform bed of a typical tractor-trailer is at the head height of seated adults in a typical passenger car, and can cause severe head trauma in even a moderate-speed collision. Around 500 people are killed this way in the United States annually.
Following the 1967 death of actress Jayne Mansfield in an auto/truck accident, the US government agency NHTSA recommended requiring a rear underride guard, also known as a "Mansfield bar", an "ICC bar", or a "DOT (Department of Transportation) bumper". They are required to be not more than 22 in (56 cm) from the road. The trucking industry has been slow to upgrade this safety feature, and there are no requirements to repair ICC bars damaged in service. However, in 1996 NHTSA upgraded the requirements for the rear underride prevention structure on truck trailers, and Transport Canada went further with an even more stringent requirement for energy-absorbing rear underride guards, and in July 2015 NHTSA issued a proposal to upgrade the US performance requirements for underride guards.
Many European nations have also required side underride guards, to mitigate against lethal collisions where the car impacts the truck from the side. A variety of different types of side underride guards of this nature are in use in Japan, the US, and Canada. However, they are not required in the United States.
SUV vs. car
Modest mismatches between SUV bumper heights and passenger car side door protection have allowed serious injuries at relatively low speeds. Unlike trucks, SUVs with bumpers more than 22 in (56 cm) from the road are legal in the United States, as are vehicles with the explosive fuel tank located behind the rear axle (see Ford Pinto). In the United States, NHTSA is studying how to address this issue as of 2014[update].
Beyond lethal interactions, repair costs of passenger car/SUV collisions can also be significant due to the height mismatch. This mismatch can result in vehicles being so severely damaged that they are inoperable after low speed collisions.
In most jurisdictions, bumpers are legally required on all vehicles. Regulations for automobile bumpers have been implemented for two reasons – to allow the car to sustain a low-speed impact without damage to the vehicle's safety systems, and to protect pedestrians from injury. These requirements are in conflict: bumpers that withstand impact well and minimize repair costs tend to injure pedestrians more, while pedestrian-friendly bumpers tend to have higher repair costs.
Although a vehicle's bumper systems are designed to absorb the energy of low-speed collisions and help protect the car's safety and other expensive components located nearby, most bumpers are designed to meet only the minimum regulatory standards.
International safety regulations, originally devised as European standards under the auspices of the United Nations, have now been adopted by most countries outside North America. These specify that a car's safety systems must still function normally after a straight-on pendulum or moving-barrier impact of 4 km/h (2.5 mph) to the front and the rear, and to the front and rear corners of 2.5 km/h (1.6 mph) at 45.5 cm (18 in) above the ground with the vehicle loaded or unloaded.
Specialized bumpers, known as "bull bars" or "roo bars", protect vehicles in rural environments from collisions with large animals. However, studies have shown that such bars increase the threat of death and serious injury to pedestrians in urban environments, because the bull bar is rigid and transmits all force of a collision to the pedestrian, unlike a bumper which absorbs some force and crumples. In the European Union, the sale of rigid metal bull bars which do not comply with the relevant pedestrian-protection safety standards has been banned.
First standards 1971
|Front and rear bumpers on Chrysler A platform cars before (left, 1971) and after (right, 1974) the US 5-mph bumper standard took effect. The 1974 bumpers are larger, heavier, and mounted farther away from the body, and they no longer contain the taillamps.|
In 1971, the US National Highway Traffic Safety Administration (NHTSA) issued the country's first regulation applicable to passenger car bumpers.[why?] Federal Motor Vehicle Safety Standard No. 215 (FMVSS 215), "Exterior Protection," took effect on 1 September 1972—when most automakers would begin producing their model year 1973 vehicles. The standard prohibited functional damage to specified safety-related components such as headlamps and fuel system components when the vehicle is subjected to barrier crash tests at 5 miles per hour (8 km/h) for front and 2.5 mph (4 km/h) for rear bumper systems. The requirements effectively eliminated automobile bumpers designs that featured integral automotive lighting components such as tail lamps.
In October 1972, the US Congress enacted the Motor Vehicle Information and Cost Saving Act (MVICS), which required NHTSA to issue a bumper standard that yields the "maximum feasible reduction of cost to the public and to the consumer". Factors considered included the costs and benefits of implementation, the standard's effect on insurance costs and legal fees, savings in consumer time and inconvenience, as well as health and safety considerations.
The 1973 model year passenger cars sold in the US used a variety designs. They ranged from non-dynamic versions with solid rubber guards, to "recoverable" designs with oil and nitrogen filled telescoping shock-absorbers.
The standards were further increased for the 1974 model year passenger cars with standardized height front and rear bumpers that could take angle impacts at 5-mile-per-hour (8 km/h) with no damage to the car's lights, safety equipment, and engine. This often meant additional overall vehicle length, as well as new front and rear designs to incorporate the stronger energy absorbing bumpers. Passenger cars featured gap-concealing flexible filler panels between the bumpers and the car's bodywork causing them to have a "massive, blockish look". A notable exception that year was the new AMC Matador coupe that featured "free standing" bumpers with rubber gaiters alone to conceal the retractable shock absorbers.
Regulatory effect on design
|US (left) and rest-of-world (right)|
|Front bumpers on Mercedes-Benz W116 (top), BMW E28 5-series (middle), Lamborghini Countach (bottom): The US bumpers are more massive and protrude farther from the bodywork.|
Cars for the US market were equipped with bulky, massive, heavy, protruding bumpers to comply with the 5-mile-per-hour bumper standard in effect from 1973 to 1982. US bumper height requirements effectively made some models, such as the Citroën SM, ineligible for importation to the United States.
Zero-damage standards 1976
The requirements promulgated under MVICS were consolidated with the requirements of Federal Motor Vehicle Safety Standard Number 215 (FMVSS 215, "Exterior Protection of Vehicles") and promulgated in March 1976. This new bumper standard was placed in the United States Code of Federal Regulations at 49 CFR 581, separate from the Federal Motor Vehicle Safety Standards at 49CFR571. The new requirements, applicable to 1979-model year passenger cars, were called the "Phase I" standard. At the same time, a zero-damage requirement, "Phase II", was enacted for bumper systems on 1980 and newer cars. The most rigorous requirements applied to 1980 through 1982 model vehicles; 5 miles per hour (8 km/h) front and rear barrier and pendulum crash tests were required, and no damage was allowed to the bumper beyond a 3⁄8 in (10 mm) dent and 3⁄4 in (19 mm) displacement from the bumper's original position.
Cost benefit analysis leads to new standards 1982
NHTSA amended the bumper standard in May 1982, halving the front and rear crash test speeds for 1983 and newer car bumpers from 5 miles per hour (8 km/h) to 2.5 miles per hour (4 km/h), and the corner crash test speeds from 3 miles per hour (5 km/h) to 1.5 miles per hour (2 km/h). In addition, the zero-damage Phase II requirement was rolled back to the damage allowances of Phase I. At the same time, a passenger car bumper height requirements of 16 to 20 inches (41–51 cm) was established for passenger cars.
NHTSA evaluated the results of its change in 1987, noting it resulted in lower weight and manufacturing costs, offset by higher repair costs.
As discussed in detail under Physics, prior to 1959, people believed the stronger the structure, the safer the car. Such rigid construction proved deadly to passengers, because the force from impact went straight inside the vehicle and onto the passenger.
Despite these findings, consumer and insurance groups both decried the weakened bumper standard, arguing that it increased overall consumer costs without any attendant benefits except to automakers. In 1986, Consumers Union petitioned NHTSA to return to the Phase II standard and disclose bumper strength information to consumers. In 1990, NHTSA rejected that petition.
As an example, in 1990 the Insurance Institute for Highway Safety conducted four crash tests on three different-year examples of the Plymouth Horizon. The results illustrated the effect of the changes to the US bumper regulations (repair costs quoted in 1990 United States dollars):
- 1983 Horizon with Phase-II 5-mph bumpers: $287
- 1983 Horizon with Phase-I 2.5-mph bumpers: $918
- 1990 Horizon: $1,476
A market failure is created when consumers are not able to choose autos based on better/worse repair costs. In the United States, the Insurance Institute for Highway Safety subjects vehicles to low speed barrier tests (6 mph/10kph) and publicizes the repair costs. Car makers that do well in these tests will publicize them.
Canada's bumper standard, first enacted at the same time as that of the United States, was generally similar to the US regulation. However, the Canadian standard was not weakened from 8 km/h (5 mph) to 4 km/h (2.5 mph) in accord with the weakened US standard of 1983. Some automakers chose to provide stronger Canadian-specification bumpers throughout the North American market, while others chose to provide weaker bumpers in the US market, which hampered private importation of vehicles from the US to Canada.
In early 2009, Canada's regulation shifted to harmonize with US Federal standards and international ECE regulations. Consumer groups are upset with the change, but Canadian regulators assert that the 4 km/h (2.5 mph) test speed is used worldwide and is more compatible with improved pedestrian protection in vehicle-pedestrian crashes.
|Wikimedia Commons has media related to Bumpers.|
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