||The examples and perspective in this article deal primarily with North America and do not represent a worldwide view of the subject. (March 2009)|
Bumpers also have two occupant safety functions: minimizing height mismatches between vehicles, and protecting pedestrians from injury.
- 1 Construction
- 2 Physics
- 3 Pedestrian safety
- 4 Height mismatches
- 5 Repair cost publicity
- 6 Regulation
- 7 See also
- 8 References
- 9 Further reading
Bumpers were originally a rigid metal bar.
In 1968, Pontiac innovated a front bumper designed to absorb impact without permanent deformation at low speeds. This body color plastic bumper was known as the Endura bumper. It was introduced on the Pontiac GTO, and appeared in a notable television commercial where John DeLorean hit the new car with a sledgehammer without damage.
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.
Specialized bumpers, known as "bull bars" or "roo bars", protect vehicles in rural environments from collisions with large animals. However, studies have shown that bull bars cause an increase in the risk of death and serious injury to pedestrians in urban environments. This is 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; the sale of rigid metal bullbars which do not comply with the European Union standards has been banned.
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. Modern theories of occupant protection point in the opposite direction, towards vehicles that crumple progressively. A completely rigid vehicle could have excellent bumper protection for vehicle components, but would sacrifice 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. On front-end bumpers especially, designers have lowered them, and have used softer materials, such as foams and crushable plastics to reduce the severity of impact on legs.
The height and placement of bumpers may be 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 in this manner 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 no more than 22 in (56 cm) from the road. The trucking industry has been slow to upgrade this safety feature. There are no requirements to repair ICC bars damaged in service.
Many European nations have also required side underride guards, to mitigate against lethal collisions where the car impacts the truck from the side. These 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 damage can result in vehicles being so severely damaged that they are inoperable after low speed collisions.
Repair cost publicity
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. This counteracts the market failure that would exist if consumers were not able to choose cars based on better/worse repair costs. Car makers that do well in these in these tests will publicize them.
As an example, in 1990, IIHS 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
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 - 'strong' bumpers minimize economic damage, while 'soft' bumpers minimize injury.
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.
||The neutrality of this article is disputed. (June 2015)|
||This article has no lead section. (June 2015)|
|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 to comply with the 5-mile-per-hour bumper standard imposed by NHTSA, in effect from 1973 to 1982. Other models, such as the Citroën SM, were de facto banned by this regulation.
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 49CFR581, 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.
Facing pressure from automakers, and operating under the Reagan administration's pledge to use cost–benefit analysis to reduce regulatory burdens on industry, NHTSA most recently 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. At that time, NHTSA promised to conduct research and testing to provide consumers with accurate information on the quality of new car bumpers, but no such information has been provided.
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.
On the economic issue of repair costs, standards were developed under the international safety regulations were originally developed as European standards and now 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.
|Wikimedia Commons has media related to Bumpers.|
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- http://www.scienceservingsociety.com/ts/text/ch11.htm The reduction in speed divided by the time over which it takes place defines deceleration. Injury-producing forces are proportional to the deceleration experienced by the occupant. Occupant protection aims at reducing these forces by spreading the occupant's changes in speed over longer times. The theoretical best protection would be for the occupant to slow down from the initial vehicle speed to zero speed at a constant deceleration using the entire distance between the occupant's body and the vehicle's point of impact. In the previous example of an initial speed of 50 km/h, and assuming the driver is seated 2.5 m behind the front bumper, the resulting average deceleration would be 4 G, uncomfortable but unlikely to produce even a minor injury.
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