The Illinois Department of Transportation has periodically conducted pavement longevity studies to assess the longevities and the traffic loadcarrying capacities of these new and rehabilitated pavements so that any needed improvements to design, construction, or rehabilitation could be identified and implemented in a timely manner. The results of the latest round of pavement longevity studies in Illinois provide performance data updated through 2000 for new hot-mix asphalt concrete (HMAC), jointed reinforced concrete pavement (JRCP), and continuously reinforced concrete pavement (CRCP) construction as well as the asphalt concrete (AC) overlays (first, second, and third overlays) of these original pavements. These studies were conducted on more than 2,000 centerline miles of Interstate and other freeways that were constructed beginning in the 1950s in Illinois. Significant findings on the performance of the original pavements and overlays were obtained, and these findings will be of value to designers and managers to improve pavement cost-effectiveness and life. Survival curves have an economic impact on the agency. Key findings show the impact of pavement type (HMAC, JRCP, or CRCP), slab thickness, geographic location (north or south), durability cracking (D-cracking), and AC overlay thickness (coupled with preoverlay condition) on longevity and load-carrying capacity. The results of the probabilistic analysis illustrate the wide variation in pavement life and traffic carried. The study also provides models for predicting the probability of survival for various designs of original pavements and AC overlays in Illinois for use in pavement management.