Interpretation ID: nht70-2.24

DATE: 09/03/70

FROM: AUTHOR UNAVAILABLE; Douglas W. Toms; NHTSA

TO: General Motors Corporation

TITLE: FMVSR INTERPRETATION

TEXT: On August 13, 1970, you petitioned, on behalf of General Motors Corporation, for reconsideration of the amendment of 49 CFR 571.3, published on July 14, 1970 (35 F. R. 11242), which established a definition of "fixed collision barrier". The views presented in your petition have been carefully considered. For the reasons stated below, your petition is denied.

You argued that the phrase "absorb no significant portion of the vehicle's Kinetic energy" was subjective, and therefore not in accord with the statutory requirement that standards be stated in objective terms. This argument is without merit. It appears to be based on the misconception that the purpose of the definition is to describe, or prescribe standards for, a manufacturer's test barrier, as evidenced by your statement that it "gives manufacturer no guidelines for determing whether or not he has built a barrier which complies with the definition." The Bureau does not intend that manufacturers should build barriers to "comply with the definition." As stated in the notice,

"this is not intended to be a description of an actual test barrier. It is a device used in various standards to establish required quantitative performance levels of a vehicle in a crash situation, and means simply that the vehicle must meet the requirement no matter how small an amount of energy is absorbed by the barrier."

Far from being subjective, the definition is mathematically precise. As the energy absorption of the barrier approaches zero as a limit, the performance characteristic being measured must remain at or above the minimum stated in the standard.

From a practical standpoint, the definition is an important aid in regulation, and is a help to all parties in that a potential source of controversy concerning compliance with the standards is removed. It simply means that when the Bureau crash-tests a vehicle, the vehicle must meet the requirement no matter what the energy-absorption properties of the barrier, and therefore there is no room for argument on the differing properties of the Bureau's and the manufacturer's test barriers. The purpose of the standards is to regulate vehicles and equipment, not test barriers; manufacturers may use whatever barriers or tests they wish to ensure compliance It is a reasonably simple matter to erect a barrier that absorbs only a minute fraction of an impacting vehicle's energy. A conscientious manufacturer should therefore have no difficulty in determining whether a particular design will meet a standard.

Your petition also argued that the definition was impracticable because

"there is no known method of measuring the amount of energy absorbed by a barrier. Therefore, there is no way that the manufacturer could even attempt to determine whether or not his barrier complied with the definition, and, more importantly, whether or not his vehicle when tested complied with the performance requirements of the standards."

The energy absorption of a barrier is a direct function of the movement of the barrier during the impact. To be sure, there are other properties, such as its effective mass and elasticity, that also are factors in energy absorption. But it is clear that as the barrier movement approaches zero, the energy absorption also approaches zero; and the barrier movement can be measured, as you indicated by your recommendation that a specified amount of movement be allowed. In all cases where the vehicle has a tangible margin of safety performance over the required minimum, therefor, a manufacturer will have no difficulty in determining that his vehicle complies,

If our standards "allowed" barrier movement, it would be far more difficult to establish conclusively that a given vehicle did not meet the standard, since it would always be open to the manufacturer to argue that the Bureau's barrier did not move as far, and consequently did not absorb as much energy, as the standard allowed. To the extent that there may be a small degree of uncertainty as to the variance is the vehicle test performance caused by the variance of a barrier from zero absorption, that uncertainty must rest with the manufacturer, who is free to design into his vehicles whatever margin of performance he desires.

This matter was thoroughly considered by the Bureau, and the opinions of knowledgeable members of the public were sought and carefully evaluated. For these reasons, your petition for reconsideration must be denied.

We appreciate your cooperation in the field of motor vehicle safety.