NDT is the collective term for evaluations conducted on an existing pavement structure that do not require subsequent maintenance work to return the pavement to its pretesting state. This is generally desirable to minimize disruption to traffic, and is essential as a screening tool to determine locations where selective material sampling should be conducted to evaluate other material properties in the laboratory. As such, its focus is to assess in situ properties that can be used to evaluate the need for further “destructive” testing (i.e., coring, boring, trenching), location of that destructive testing, and the current structural capacity of the highway as related to layer stiffness and strength. Non-destructive testing methods can assess either functional or structural condition. For NDT, data collected in the field is generally objective in nature, but engineer’s data analysis and interpretation are subjective.