The driving public's attitude toward acceptable levels of road roughness is explored using empirical data collected on urban highways. Individual driver acceptability levels are matched with international roughness index (IRI) levels to examine the existence of potential user acceptability thresholds. In particular, the observed trends are compared with the federal IRI guideline of 170 in./mi (2.7 m/km) for acceptable ride quality recommended by the Federal Highway Administration in its 1998 strategic plan for the National Highway System. The research reported on appears to provide empirical support for the federal IRI guidelines that are already in existence. This study also found that IRI levels provided a very good indication of driver acceptability, which agrees with past research based on antiquated present serviceability ratings.