"This addendum documents the investigation of the rutting bias between field data and the Highway Performance Monitoring System (HPMS)/State Department of Transportation (DOT) pavement management system (PMS) data observed in the pilot study conducted as part of the “Improving FHWA’s Ability to Assess Highway Infrastructure Health” project. The objectives of this study were to: 1) investigate the discrepancy between rutting observed from field data collection versus that retrieved from HPMS/State data to determine the cause of the bias, and 2) develop data requirements and an algorithm that can be applied to rutting to produce consistent, high-quality data. A conclusive reason for the South Dakota rutting bias found during the pilot study was identified, but one for the Minnesota data could not be identified. It is possible that the rutting bias for the Minnesota data is the result of several variables, including different gage width, different sensor types, different years of data collection, different drivers, and different vehicle types. Based on the results of this investigation, rutting data requirements such as maximum longitudinal spacing, minimum number of points collected to characterize the transverse profile, gage width, and rutting algorithms are recommended."