An Evaluation of Side Structure Improvements in Response to Federal Motor Vehicle Safety Standard 214
|NHTSA Report Number DOT HS 806 314||November 1982|
An Evaluation of Side Structure Improvements in Response to Federal Motor Vehicle Safety Standard 214
Charles J. Kahane, Ph.D.
Side door beams were installed in passenger cars in response to Federal Motor Vehicle Safety Standard 214. The purpose of beams is to reduce the velocity and depth of door intrusion into the passenger compartment in side impact crashes. The objectives of this Agency staff evaluation are to determine how many fatalities and injuries are prevented by Standard 214, to measure the actual cost of the standard, to assess cost effectiveness and to describe the actual crash performance of equipment installed in response to the standard. The evaluation is based on statistical analyses of the Fatal Accident Reporting System and National Crash Severity Study data, cost analyses of production beam assemblies and a review of staged crash tests. It was found that:
- Standard 214 eliminates 480 fatalities and 4,500 nonfatal hospitalizations per year in side impacts with fixed objects. The standard has brought about significantly shallower and wider damage patterns and has reduced occupant ejection in these crashes.
- Standard 214 eliminates 4900 nonfatal hospitalizations per year in vehicle-to-vehicle side impacts but has not reduced fatalities in these crashes. Door intrusion was significantly reduced.
- Standard 214 has added $61 (in 1982 dollars) to the lifetime cost of owning and operating a car.
Impacts to the side of a passenger car rank second only to frontal crashes as a source of occupant fatalities and serious injuries. They are especially dangerous when the impact is on the passenger compartment because there are no deep, crushable metal structures between the occupant and the impacting vehicle or object, as there are, for instance, in frontal or rear-end crashes. The door collapses into the passenger compartment and the occupants contact the door at a high relative velocity.
During the 1960's, the motor vehicle manufacturers tested various concepts for reducing penetration of the door structure into the passenger compartment. They found that the installation of a horizontal beam inside the door, accompanied by minor reinforcements of other components, significantly reduced side structure intrusion in crash tests. The beams, unlike some of the other concepts, did not change a car's external appearance and posed no problem of customer acceptance. The manufacturers developed a static laboratory test for measuring side door strength. Beams greatly improved a car's test scores. In 1970, the National Highway Traffic Safety Administration issued Federal motor Vehicle Safety Standard 214, which incorporated the static test and required all passenger cars to achieve certain minimum scores on the test, effective January 1, 1973. Beams were installed in all makes and models of cars gold in the United States since the effective date; beams were installed in many models up to 4 years before the effective date.
Executive Order 12291 (February 1981) requires agencies to evaluate their existing major regulations, including any rule whose annual effect on the economy is $100 million or more. The National Highway Traffic Safety Administration published a preliminary evaluation of Standard 214 in 1979, based on analyses of a National Crash Severity Study data file which was less than half complete at that time. Because of the limited accident sample, definitive conclusions could not be reached. A followup evaluation was promised when the data file became complete. That file has been completed and, equally important, additional data sources and new analysis techniques have become available.
This report is the Agency's reevaluation of Standard 214, superseding the findings of the 1979 study. Its evaluation objectives are:
- Calculating the benefits specifically due to Standard 214 -- lives saved and injuries prevented or reduced in severity, in side impacts -- after isolating the effect of Standard 214 from the effects of other safety standards or vehicle modifications.
- Measuring the cost of components installed or modified in response to Standard 214 in current (1979-82) production vehicles.
- Assessing cost-effectiveness.
- Comparing the effectiveness of Standard 214 in single and multivehicle crashes; for nearside and farside occupants; for impacts centered on the passenger compartment vs. other side impacts; for mitigating various specific types and sources of injury.
- Describing the effect of Standard 214 on side structure performance in highway accidents, based on analyses of vehicle damage patterns.
- Providing a physical explanation of why Standard 214 does (or does not) eliminate certain specific types of injuries in specific types of side impacts.
- Comparing the mechanisms whereby Standard 214 reduces casualties inhighway accidents to the stated rationale for the standard and to hypotheses, based on staged crashes and engineering analyses, about how the standard works.
The fatality reduction due to Standard 214 was accurately estimated by analyzing 7 years of Fatal Accident Reporting System (FARS) data. Statistical analyses of National Crash Severity Study (NCSS) data were performed to determine the number of serious injuries prevented. Nonserious injury reduction was measured from 3 years of Texas accident files. All effectiveness analyses were limited to, or emphasized, cars built just before and just after the installation of beams -- in order to isolate the casualty reduction that is specifically due to Standard 214 and to exclude reductions due to other safety standards (201, 203, 204, 205, 206, 208-210, 216) and vehicle modifications (the shift from genuine to pillared hardtops, etc.), which took place some years before or after beam installation. Multivariate statistical techniques were also used to accomplish this goal.
The analyses of the effect of Standard 214 on vehicle damage patterns and on specific types of injuries are primarily based on NCSS, supplemented, where possible, with FARS results. The cost of Standard 214 was calculated by analyzing the individual components of a representative sample of current (1979-82) cars, updating the cost estimates of the preliminary evaluation.
Engineering studies of the side impact problem and staged side impact crashes were thoroughly reviewed and discussed with Agency engineers. The review made it possible to formulate 5 specific hypotheses on how Standard 214 affects the performance of the side structure in crashes. The analyses of vehicle damage patterns and specific injury types were geared to testing these hypotheses and, finally, developing a physical explanation for the effectiveness of Standard 214 (or lack thereof) in various types of side impacts.
The most important conclusions of this evaluation are that Standard 214 has saved 480 lives per year and has significantly reduced serious injuries in side impacts with fixed objects. Standard 214 has significantly reduced serious injuries, but has had little or no effect on fatalities, in vehicle-to-vehicle side impacts -- moreover, the reduction in multivehicle crashes is primarily limited to impacts that are centered on the passenger compartment and to occupants seated adjacent to the struck side of the car. The detailed analyses of vehicle damage patterns and specific injury types established physical explanations for the effects of Standard 214 that are in complete agreement with these conclusions.
The principal findings and conclusions of the study are the following:
- In 1980, when 75 percent of the passenger cars on the highway were in compliance with Standard 214, 7800 passenger car occupants were killed in side impact crashes. There would have been 8200 fatalities if the side structure improvements required by Standard 214 had not been made (confidence bounds: 8050 to 8350); 3400 of the fatalities would have occurred in single-vehicle crashes; 4800 in multivehicle crashes.
- There would have been.74,000 fatalities and hospitalizations in side impact crashes in 1980 if Standard 214 had not been promulgated (confidence bounds: 67,000 to 80,000).
- The distribution of the serious casualties (fatalities and hospitalizations) by crash type, occupant seat location and damage location would have been:
FATALITIES & HOSPITALIZATIONS Single-Vehicle Crashes Multivehicle Crashes N Percent N Percent Nearside occupants - damage centered on compartment 7,200 36 20,000 37 Nearside occupants - damage not centered on compartment 3,400 17 11,000 20 Farside occupants 9,400 47 23,000 43 TOTAL 20,000 54,000
- The distribution of injury sources among pre-Standard 214 occupant fatalities and hospitalizations was:
Percent of Serious Injuries Contacts with side interior surfaces (doors, pillars, etc.) 49 Head injuries (including face and neck) 14 Rest of body 35 Nearside occ. in multiveh. compartment impacts 17 All other persons 18 Contacts with front interior components (dashboard, etc.) 30 Objects exterior to vehicles (mostly ejections) 8 Other 13
Fatality reduction for Standard 214
- Standard 214 reduced the risk of occupant fatality in single-vehicle side impacts by 14 percent (confidence bounds: 7 to 21 percent).
- In the preceding estimate, the definition of "single-vehicle side impact" included grade crossing accidents, rollovers with primarily side damage and complex off-road excursions. If the definition is restricted to side impacts with fixed objects, the effectiveness rises to 23 percent.
- Standard 214 had no observed effect on multivehicle crash fatalities (confidence bounds: -9 to +7 percent).
Serious casualty reduction for Standard 214
- Standard 214 reduced the risk of occupant fatality or hospitalization in side impacts, as follows:
Serious Casualty Reduction (2%) Confidence Bounds In single-vehicle crashes 25 11 to 35 In multivehicle crashes: Nearside occupants in compartment impacts 25 6 to 38 All occ. in all multivehicle crashes 8 -3 to 17
Nonserious injury reduction for Standard 214
- Standard 214 reduced drivers' risk of police-reported "visible minor" (level B) injuries, in side impacts, in Texas, as follows:
"Visible Minor" Injury Reduction (%) Confidence Bounds In single-vehicle crashes 9 -1 to 19 In multivehicle crashes 13 8 to 18
Effect of Standard 214 on depth and width of crush
- In-single-vehicle crashes the depth of crush decreased by an average of 20 percent while the width of the damaged area increased by 20 percent. In other words, Standard 214 resulted in significantly shallower and wider damage patterns.
- In multivehicle crashes centered on the compartment, the depth of crush decreased by an average of 20 percent while the width of the damaged area was unaffected. Standard 214 significantly reduced penetration without otherwise affecting the shape of the damage pattern.
- Standard 214 had no observed effect on crush patterns in multivehicle impacts that were not centered on the compartment.
Effect on location of the damaged area
- The percentage of cars in which damage was centered on the compartment was:
Percent of Cars with Damage Centered on Compartment In Single-Vehicle Crashes In Multivehicle Crashes Last 5 model years before Standard 214 50 31 First 5 model years after Standard 214 38 32
Effect on the performance of doors in crashes
- Standard 214 affected the performance of doors in side impact crashes, as follows:
Observed Effect of Standard 214 (%) In Single-Vehicle Crashes In Multivehicle Crashes Reduction of occupant ejection through doors 40 - 60 10 - 50 Reduced incidence of doors opening in crashes 20 - 40 10 - 30 Reduced incidence of latch or hinge damage 10 - 20 0 - 5
Effect on sill override
- Standard 214 reduced the incidence of sill override in multivehicle crashes by about 20 percent.
Effectiveness of Standard 214 - by injury source
- In collisions with fixed objects, Standard 214 reduction fatalities by 24 percent and nonejection fatalities by 22 percent. Both reductions are statistically significant
- The reduction of serious injuries (resulting in fatality or hospitalization), by injury type, was:
Observed Reduction for Standard 214 (%) In Single-Vehicle Crashes In Multivehicle Crashes Contacts with side interior surfaces (doors, etc.) 36 10 Head Injuries (incl. face and neck) 25 1 Rest of Body 41 14 Nearside occ. in compartment impacts 50 33 All other persons 23 -10 Contacts with front interior components (steering assembly, etc.) 27 0 Objects exterior to vehicles (mostly ejections) 63 57
Benefits of Standard 214
- The annual benefits of Standard 214, when all cars on the road meet the standard, will be:
Best Estimate Confidence Bounds LIVES SAVED - in single vehicle crashes 480 300 to 600 NONFATAL HOSPITALIZATION ELIMINATED In single vehicle crashes 4,500 900 to 8,200 In multivehicle crashes 4,920 800 to 9,000 TOTAL 9,470 4,300 to 14,700 "VISIBLE MINOR" (LEVEL B) INJURIES ELIMINATED -- Multivehicle 15,000 -------------
Cost of Standard 214
- Standard 214 added an average of $30 (in 1982 dollars) to the purchase price of current (1979-82) cars.
- It increased the weight of a car by 28 pounds.
- The total lifetime cost of Standard 214 (including fuel consumption due to the weight increase) is $61 per car (in 1982 dollars).
- An "Equivalent Fatality Unit" corresponds to 1 fatality or 16.9 nonfatal hospitalizations. Standard 214 eliminates 1.7 Equivalent Fatality Units per million dollars of cost (confidence bounds: 1.1 to 2.3).
Single-vehicle side impacts
- Standard 214 has significantly reduced fatalities and serious injuries in single vehicle crashes.
- The standard has helped cars "glance by" fixed objects, limiting the damage in the compartment area and spreading it to less vulnerable regions of the car. It has reduced the overall severity of the collision, not only for persons sitting next to the damaged area but also, to a lesser extent, for the other occupants.
- It has thereby also helped protect the integrity of the door structure, significantly reducing the risk of occupant ejection, even in potentially fatal crashes.
- The standard has accomplished the goal of reducing nearside occupants' torso, arm and leg injuries due to contact with the car's side structure.
- But the standard's benefits also extend to head injuries, contacts other than the side structure, and farside occupants, because it has made crashes generally less severe and it has reduced ejection. For these reasons, it has significantly reduced fatalities as well as nonfatal serious injuries.
Multivehicle side impacts
- Standard 214 has significantly reduced nonfatal serious injuries and nonserious injuries in multivehicle crashes.
- It has had little or no effect on fatalities.
- The standard has reduced side structure intrusion when the car is directly impacted in the compartment by another vehicle. The reduction is primarily a consequence of increased crush resistance.
- It does not appear to significantly promote deflection of the striking vehicle -- the effect that was prominently displayed in fixed object collisions.
- The standard may have been partially effective in preventing the striking vehicle from overriding the sill. This effect, at best, accounts for only a small portion of the standard's benefit in multivehicle crashes.
- The standard may have reduced occupant ejection -- a mechanism that accounts for a much smaller percentage of the injuries in multivehicle than in single vehicle crashes.
- The standard has accomplished its goal of significantly reducing nearside occupants' torso, arm and leg injuries due to contact with side structures in compartment impacts. These lesions constitute a large portion of the serious nonfatal injuries but a much smaller portion of the fatalities.
- But the standard appears to have had negligible effect on all other types of injuries (except, possibly, ejections).
- The standard has had negligible effect on fatalities, primarily, because it has not significantly reduced head injuries and also, perhaps, because the added crush resistance in the doors, without other major modifications, is of little use in extremely severe crashes.
- Although Standard 214 has had significant benefits in multivehicle crashes, they are exceeded by the benefits in single vehicle crashes.