In the present study, we analyzed field measurement data obtained for a Japanese expressway and used it as a data set for the validation of microscopic simulation models. Consequently, in accordance with previous studies, we confirmed the common features depicted by the fundamental diagram (flux vs density relation) and lane-usage ratio vs density diagram. We found two things regarding lane-changing behavior: (1) a lane change occurs asymmetrically, where a lane change from a slow to a fast lane differs from that from a fast to a slow lane; and (2) the so-called incentive criterion in the case of small gaps between the preceding vehicles in both slow and fast lanes refers to the velocities and /or the relative velocities with respect to the preceding vehicles, whereas that for relatively large gaps refers to the distances to the preceding vehicles is cast into the above incentive criterion in addition to the two factors mentioned above.