The National Airport Pavement Test Facility (NAPTF) is a fully enclosed instrumented test track 274.3 m (900 ft) long by 18.3 m (60 ft) wide. In construction cycle three (CC3), four new flexible pavement test items (LFC1 through LFC4) were constructed. The pavement structures were of conventional construction with 127-mm (5-in) asphalt surface, 203-mm (8-in) crushed stone base, varying subbase thickness, and a silty clay subgrade of 3 to 4 CBR. The test items were named LFC1 (thinnest subbase) through LFC4 (thickest subbase). Traffic tests were performed with 6-wheel loading in one wheel track and 4-wheel loading in the other wheel track. Rut depth and profile measurements were made on the asphalt surface during traffic testing. A fixed wander pattern was applied to the traffic during the tests. The wander pattern consisted of 66 repetitions, 33 traveling east and 33 traveling west. Sensors were embedded into the pavement layers to measure the pavement response to applied loads and included asphalt strain gages (ASG), multiple depth deflectometers (MDD), and soil pressure cells (PC). Subgrade pressure cells (2 inches, Kulite) were placed only in test item LFC4 and were placed 10 cm (4 inches) and 43 cm (17 inches) below the subgrade surface. This paper summarizes the subgrade vertical stress measurements under 6-wheel and 4-wheel landing gears at 245 kN (55,000 lb) and 289 kN (65,000 lb) wheel loads at different wander positions. There was no evidence of structural failure in LFC4 at the end of traffic testing.