SUPPLEMENTARY INFORMATION:

Background

On July 11, 2008, NHTSA published a final agency decision notice (73 FR 40016) announcing enhancements to the National Highway Traffic Safety Administration's New Car Assessment Program (NCAP), which provides consumers with comparative information on the safety of new vehicles to assist them with vehicle purchasing decisions and to encourage motor vehicle manufacturers to make safety improvements. In the area of crashworthiness safety (how well the vehicle protects occupants in the event of a crash), NCAP uses the 5-Star Safety Rating system to communicate the relative performance of vehicles to consumers. In the 2008 final agency decision notice, the agency discussed how the star ratings are determined based on the relative risk of injury to occupants, quantified as Relative Risk Scores (RRS). The notice discussed the determination of the RRS and the use of ASTM E29 “Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications” (ASTM E29) to round values. In actuality, since current NCAP requirements were instituted beginning with the 2011 model year, NHTSA has been using the traditional rounding method, in which the following rounding logic is used:

• When the digit after the last digit to be retained is less than 5, keep the last digit unchanged (for example, in rounding to the hundredths place: 0.453 = 0.45).
• When the digit after the last digit to be retained is greater than or equal to 5, increase the last retained digit by 1 (for example, in rounding to the hundredths place: 0.455 = 0.46 and 0.465 = 0.47).

The ASTM E29 method and the traditional rounding method only differ in instances when the digit after the last place to be retained is equal to 5 and there are no digits beyond 5 (for example, when rounding a number such as 0.455 to the hundredths place). The following rounding logic is used in ASTM E29 and is known as the round-to-even method:

• When the digit after the last digit to be retained is equal to 5, increase the last retained digit by 1 if it is odd, or leave the last retained digit unchanged if it is even (for example, in rounding to the hundredths place: 0.455 = 0.46 and 0.465 = 0.46).

Need for Correction

While the agency referred in the final agency decision notice to the ASTM E29 method, the traditional rounding method has been and is the method used in NCAP. The traditional rounding method is also used in the publicly-available ratings calculator that the agency releases each year, which includes injury measures collected from NCAP's vehicle tests.^[1]

Following publication of the final agency decision notice, the agency was asked about its method of rounding injury values obtained from its vehicle tests. This notice reiterates the agency's longstanding rounding method, which is the traditional rounding method (not the ASTM E29 method), used in all NCAP-related calculations to generate vehicle safety ratings.

79 FR 28594