National Traffic Fatality and Injury Reduction Act of 1991

National Traffic Fatality and Injury Reduction Act of 1991 - Authorizes the Secretary of Transportation to make grants for traffic safety programs to States which require any person riding a motorcycle to wear a helmet and any driver or front seat passenger of a passenger car to have seat belts properly fastened. Authorizes appropriations.

Requires States receiving grants to agree to maintain at least their average levels of expenditures for traffic safety programs over the preceding two fiscal years.

Prohibits a State from receiving such a grant in more than three fiscal years. Specifies the Federal share of grants and the aggregate amount of such grants to each State.

Sets forth requirements with respect to: (1) States' eligibility for grants; and (2) measurement of compliance with State safety laws.

Eliminates a provision prohibiting a highway safety program approved by the Secretary from requiring that motorcycle operators or passengers 18 years or older wear a safety helmet.

Requires any State where it is lawful to operate or ride a motorcycle without wearing a motorcycle helmet or to occupy a front seating position in a passenger car without using a safety belt or child restraint system to expend a specified percentage of its apportioned Federal aid highway funds for highway safety programs.