This paper examines the history of traffic data collection activities used by the US Federal Highway Administration's Long-Term Pavement Performance (LTPP) Program. The authors explore the program's evolution, beginning with its original plan in the late 1980s when it envisaged highway agencies' use of low cost traffic data collection systems at 2,500 test sites. When this plan became no longer viable, a new plan was developed to collect research quality traffic data from fewer sites, a strategy that has resulted in the collection of the largest repository of high-quality traffic data ever seen. In addition to the LTPP program's data collection history, technical details of the revised plan are presented, as are financing and contracting arrangements and a summary of results.