Traffic performance on two-lane rural highways is commonly characterized by percent time spent following (PTSF), a parameter that determines the level of service on a road segment. Although PTSF is frequently used by transportation engineers and researchers, there is no agreement about its estimation method and values. Therefore, a study was done to calibrate and compare models of PTSF with the data collected on 25 segments of 15 two-lane highways in Israel. The study showed large differences between the collected models and previous model values. Furthermore, the study estimated traffic intensity, which was an additional characteristic of the driver-following phenomenon; this variable did not approach its expected value of 1.0. This lack of agreement between actual and expected values may result from changing driver behavior, that is, impatience as platoon lengths and delays increase. To avoid long platoons, drivers prefer to travel between them and then to perform a passing maneuver sooner than expected. This phenomenon not only reduces platoon length and delays, but also increases the risk of serious and fatal crashes.