An Evaluation of Federal Motor Vehicle Safety Standards for Passenger Car Steering Assemblies

Standard 203 - Impact Protection for the Driver

Standard 204 - Rearward Column Displacement

Charles J. Kahane, Ph.D.

Energy absorbing steering columns were installed in passenger cars in response to Federal Motor Vehicle Safety Standard 203. The columns are designed to compress at a controlled rate, cushioning the impact of the driver's chest in frontal crashes. Standard 204 specifies requirements limiting the rearward displacement of the steering wheel toward the driver. The objectives of this Agency evaluation are to determine how many driver fatalities and injuries are prevented by Standards 203 and 204, to measure the actual cost of the standards, to assess cost effectiveness and to describe the actual crash performance of equipment installed in response to the standards. The evaluation is based on statistical analyses of Fatal Accident Reporting System and National Crash Severity Study data, cost analyses of actual steering assemblies and a review of laboratory and crash tests and multidisciplinary accident investigations. It was found that

• Standards 203 and 204 are cost-effective and have significantly reduced driver fatalities and injuries in frontal crashes. They will annually prevent 1300 fatalities and 23,000 nonfatal injuries requiring hospitalization when all cars comply.

• Standards 203 and 204 have added $10 to the lifetime cost of owning and operating a car.

• Energy absorbing steering assemblies have been partially successful in cushioning the driver, but their performance is degraded under nonaxial loads.

• Standard 204 has substantially reduced rearward displacement of the steering column in crashes.

The steering assembly is the most common source of serious injury for drivers involved in frontal crashes. In passenger cars built before the 1967 model year, the steering column was a rigid pole ending in a narrow hub. In frontal crashes, the driver would hit the rigid column, his load concentrated on the narrow hub. Even worse, in some crashes the steering column was propelled rearwards, toward the driver, at a high rate of speed. Steering wheels and spokes were weak and brittle and contained hazardous metal attachments.

During the 1960's, the motor vehicle manufacturers, in cooperation with the. safety research community, developed energy absorbing columns that collapsed at a controlled rate when the driver hit them. Methods were discovered to prevent the rearward displacement of the column in crashes and safer steering wheels were designed. The General Services Administration established criteria for testing the performance of the improved steering assemblies under controlled conditions. These performance criteria became Standard 515/4a for Government vehicles. In 1967, the National Highway Traffic Safety Administration extended the requirements to all passenger cars sold in the United States, effective January 1, 1968. The requirements were promulgated as Federal Motor Vehicle Safety Standards 203 and 204. All passenger cars since model year 1968, as well as many 1967 models, appear to have met the Standards. In addition, the manufacturers have voluntarily made some improvements in the steering wheels that were not strictly required for compliance with the Standards.

Executive Order 12044 (March 1978) and Department of Transportation Order 2100.5 (May 1980) called for a review and evaluation of existing major regulations. This study is an evaluation of the vehicle modifications made in response to Standards 203 and 204, based on the actual operating experience of passenger cars. The evaluation objectives are

(1) Calculating the overall benefits of the vehicle modifications - life savings and injury severity reduction - treating Standard 203, Standard 204.and the voluntary steering wheel improvements as a single unit.

(2) Measuring the actual cost of the modifications.

(3) Assessing cost-effectiveness.

(4) Comparing the compliance test requirements to the performance of post-Standard vehicles in highway accidents.

(5) Explaining why the Standards have been effective; assessing the benefit for each specific vehicle modification and the mechanism whereby it produces benefits.

(6) Identifying the principal shortcomings of the current Standards vehicle improvements whose benefits did not meet expectations.

(7) Identifying areas in which Standards 203 and 204 could potentially be improved.

The fatality reduction due to Standards 203 and 204 was estimated by analyzing 5 years of Fatal Accident Reporting System (FARS) data. Statistical analyses of National Crash Severity Study (NCSS) data - 11,840 accident cases were on file as of November 1979 - were performed to determine the number of serious injuries prevented. The Multidisciplinary Accident Investigation (MDAI) file provided information on steering column compression. The cost of Standards 203 and 204 was calculated by analyzing the individual components of a representative sample of steering assemblies.

The results from the FARS, NCSS and MDAI analyses were compared to previously published statistical studies of Standards 203 and 204. Laboratory and crash test results were reviewed, as were clinical analyses of selected accident cases. The research, rulemaking and enforcement activities related to the two Standards were discussed with Agency engineers. The conclusions of this evaluation are based on all of the information sources - statistical, clinical and engineering.

The most important and definitive conclusions of this evaluation are that Standards 203 and 204 have reduced the number of driver fatalities and serious injuries in frontal crashes. Standard 204 has decreased rearward displacement of the steering column. These conclusions are based on statistically significant and consistent findings from a wide variety of data files. The statistical findings, moreover, were uniformly consistent with engineering intuition and clinical analyses.

The findings on some of the detailed analyses, such as the effectiveness of specific types of energy-absorbing devices, were not statistically significant because they involved splitting the data into subsamples. Conclusions based on those findings are less than definitive.

The conclusions on why the Standards have been effective, how much each hardware improvement has contributed to benefits and what could be done to enhance effectiveness must be considered speculative. These conclusions are intuitive judgments based on a thorough review of engineering analyses, selected accident cases, test results and statistical tabulations.

The evaluation suffers from the inherent shortcoming of a "before-after" design. The pre-Standard cars - model year 1967 and earlier - are quite a few years older than the post-Standard cars on the accident data files. A major portion of the analysis was devoted to identifying and removing the resulting biases. Several independent tests which were performed an the data files appear to suggest that the age biases and other confounding factors may have been successfully removed.

The missing data rate on injury-causing contact points was high (30 percent) in the National Crash Severity Study and it varied from one team to another. It was necessary to devise analytic techniques for removing the consequent biases. The NCSS file did not contain information on steering column compression, thereby precluding a rigorous statistical comparison of injury severity and column compression.

In general, though, the findings and conclusions of this evaluation may be viewed with confidence because of the harmony between the statistical results, in-depth findings and engineering intuition. Earlier studies of Standards 203 and 204 were largely consistent with the NCSS, FARS, and MDAI analyses performed for this evaluation. Many of the principal findings were supported by two or more independent analysis procedures or data sources.

The principal findings and conclusions of the study are the following:

The problem

• In 1978, when nearly 90 percent of the passenger car fleet complied with Standards 203 and 204, 41,400 drivers of passenger cars were killed or hospitalized as a result of contact with the steering assembly during a crash. This number would have increased to 63,000 if the steering assembly improvements required by Standards 203 and 204 had not been made.

Effectiveness and benefits of Standards 203 and 204 - fatalities

• The equipment installed in response to Standards 203 and 204 (including voluntary steering assembly improvements not strictly required for compliance) reduced the overall risk of driver fatality in a frontal crash by 12 percent (confidence bounds: 8.5 to 15.5 percent).

• If all passenger cars had complied with Standards 203 and 204 in 1978, there would have been 1300 fewer driver fatalities than if none of the be cars had complied (confidence bounds: 900 to 1800).

Effectiveness and benefits of Standards 203 and 204 - serious injuries

• The equipment installed in response to Standards 203 and 204 reduced the risk of serious injury due to steering assembly contact by 38 percent (confidence bounds: 28 to 48 percent). An injury is defined to be "serious" it it causes the driver's death or at least overnight hospitalization.

• Since 46 percent of the driver fatalities and hospitalizations in frontal crashes were principally due to the steering assembly (i.e., no serious injuries from any other contact source), Standards 203 and 204 reduced the overall risk of serious driver injury in a frontal crash by 17.5 percent (i.e., 46% of 38%).

• If all passenger cars had complied with Standards 203 and 204 in 1978, 24,200 fewer drivers would have sustained serious injury caused by contacting the steering assembly than if none of the cars had complied (confidence bounds: 14,900 to 33,500).

Cost of Standards 203 and 204

• The average lifetime consumer cost per car, for cars built during 1968-78, was:

  Modifications needed for meeting the Standards	$ 8.87
  Voluntary steering wheel improvements	.33
  Fuel consumption due to 1.11 pound weight increase	1.26
  TOTAL	$10.46	(in 1978 dollars)

• There were no substantial differences among the principal designs of energy absorbing steering systems in regard to their cost and weight.

Cost-effectiveness

• An "Equivalent Fatality Unit" corresponds to 1 fatality or 20 injuries requiring overnight hospitalization. Standards 203 and 204 eliminate 23.8 Equivalent Fatality Units per million dollars of cost (confidence bounds: 18.2 to 29.4).

Displacement of the steering column into the passenger compartment

• The steering column was displaced rearwards in 18 percent of the pre-Standard cars in which the driver was seriously injured by the steering assembly.

• Standard 204 reduced rearward column displacement by a statistically significant 81 percent.

• The steering column was displaced upwards or sideways in 3 percent of the pre-Standard cars in which the driver was seriously injured by the steering assembly.

• The incidence of gross upward or sideways column displacement in crashes is too low to allow a statistically significant comparison between pre- and post-Standard cars even though the incidence was observed to be 68 percent higher in the post-Standard cars.

The Problem

• Standards 203 and 204 addressed themselves to specific, quantifiable motor vehicle safety problems of major importance.

Overall effectiveness

• The equipment installed or modified in response to Standards 203 and 204 has reduced driver fatalities in frontal crashes.

• It has reduced serious nonfatal injuries to drivers in frontal crashes.

• Standards 203 and 204 are cost-effective.

Why have Standards 203 and 204 been effective?

• Standard 204 has been highly effective in reducing rearward steering column displacement. This factor accounts for about 1/3 to 1/2 of the total injury reduction and an even higher fraction of the total fatality reduction for Standards 203 and 204, combined.

• The energy absorbing devices installed in response to Standard 203 are successfully compressed (3 inches or more) in about half the crashes in which they are heavily impacted by the driver. This factor accounts for about 1/4 to 1/3 of the total injury reduction and an even larger fraction of the total fatality reduction for Standards 203 and 204 combined.

• The improvements to steering wheels that manufacturers voluntarily made at about the time that Standards 203 and 204 took effect - hub padding, removal of horn rings, stronger rims and spokes have substantially reduced arm and head injuries. They have also contributed to the effective operation of the energy absorbing devices. They account for about 1/3 of the overall injury reduction (but a much smaller fraction of the fatality reduction) for Standards 203 and 204, combined.

• The significant steering assembly contact injury reduction due to Standards 203 and 204 and the successful or partially successful and performance as intended, in crashes, by each of the major equipment modifications is proof that the compliance test conditions are relevant to some aspect of actual highway performance.

Shortcomings of Standards 203 and 204

• The principal shortcoming of Standards 203 and 204 has been the failure of the energy absorbing devices to compress in about half the crashes in which they are heavily impacted by drivers.

• Energy absorbing devices and other steering assembly components tend to bind rather than compress when they are exposed to nonaxial loads.

• Nonaxial loads may be a consequence of initial vehicle damage, unfavorable driver kinematics, upward steering column displacement, for unfavorable steering wheel spoke alignment or oblique frontal crash forces.

• Standard 204 has not reduced the incidence of steering column displacement in a primarily upwards or sideways direction.

• The improvements to the spokes, rim and face of steering wheels were largely voluntary. Since they are not required for compliance, they have not been uniformly applied to the vehicle fleet.

Side effects of Standards 203 and 204

• The Standards do not appear to have had negative side effects: there was no increase in serious injury from contact points other than the steering assembly.

Comparison of alternative energy absorbing devices

• The six major designs of energy absorbing devices are about equally effective in reducing serious injuries.

• The various devices did not differ substantially in their tendency to bind under driver load.

• They all cost approximately the same.

• A British study concluded that the steering wheel canister is more effective and more easily compressible than the energy absorbing columns. This evaluation does not support their conclusion.

Potential for improving Standards 203 and 204

• There may be potential benefits in extending the Standard 203 requirements, which currently simulate energy absorbing device performance only under nearly axial column load, to include tests that simulate nonaxial loading situations.

• For substantially increased benefits, it may be necessary to realistically simulate many of the conditions that lead to nonaxial loading, such as initial vehicle damage, unfavorable driver kinematics, upward steering column displacement, unfavorable steering wheel spoke alignment and oblique frontal crash forces.

• Upward column displacement, even in small amounts, can aggravate column binding. In larger amounts, it can magnify head injury risk. There may be potential benefits in modifying the requirements of Standards 203 and 204 to reduce both types of hazard associated with upward column displacement.

• The voluntary steering wheel improvements have not been uniformly implemented. There may be potential benefits in adding performance requirements to Standard 203 that would result in the use of crashworthy steering wheels in the entire vehicle fleet.