49 CFR Part 571. 218 A notice of proposed rulemaking (NPRM) amending FMVSS No. 218 was published on May 21, 2015 (80 FR 29458). The NPRM set forth an interpretation of the definition of “motor vehicle equipment” in the United States Code, as amended by the Moving Ahead for Progress in the 21st Century (MAP–21) Act, and requested comments on two proposed changes to the motorcycle helmet safety standard, FMVSS No. 218. NHTSA proposed to add a definition of “motorcycle helmet” and modify the existing performance requirements of the standard by adding a set of dimensional and compression requirements. These requirements and the associated test procedures would identify those helmets whose physical characteristics indicate that they likely cannot meet the existing performance requirements of the standard. Third, NTHSA proposed an optional alternative compliance process for manufacturers whose helmets do not comply with the proposed dimensional and compression requirements, but do comply with the performance requirements and all other aspects of FMVSS No. 218 . If this proposal is adopted, NHTSA will publish a list of helmets that have complied with the alternative compliance process and can therefore be certified by their manufacturers. The NPRM was the result of the agency’s assessment of other actions that could be taken to further increase the percentage of motorcyclists who wear helmets that comply with the helmet standard.