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Condition of U.S. Roadways by Functional System
Numbers may not add to totals due to rounding.
This edition of this table is not comparable to 2015 or previous editions due to a change in the categories of road conditions.
Data is reported as the International Roughness Index (IRI) in inches per mile. Lower IRI represents smoother riding roadways. For more information on the rating system, refer to National Cooperative Highway Research Program (NCHRP) report 20-24(37)G, Technical Guidance for Deploying National Level Performance Measurements, available at http://onlinepubs.trb.org/onlinepubs/nchrp/docs/NCHRP20-24(37)G_FR.pdf as of June 2015.
KEY: N = data do not exist; U = data are not available.
U.S. Department of Transportation, Federal Highway Administration, Highway Statistics (Washington, DC: Annual Issues), tables HM-63 and HM-64, available at https://www.fhwa.dot.gov/policyinformation/statistics.cfm as of Dec. 3, 2020.