The Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU) of 2005 directed the Secretary of Transportation to transmit a report to Congress by August 2007 on research conducted to address tire aging, and include a summary of the findings and recommendations. NHTSA conducted a multi-year research program on the aging of tires used on passenger cars, light trucks, and vans, which evaluated several accelerated tire aging methods to determine their relative effectiveness in replicating the characteristics of tires undergoing aging in the field.