The performance of “thin membrane surface” (TMS) highways is largely controlled by the strength of the subgrade soil, which in turn is a function of matric suction. Thermal conductivity matric suction sensors were used to indirectly measure in situ matric suctions. In September 2000, 32 thermal conductivity sensors were installed under TMS highways at two locations; namely, Bethune and Torquay, Saskatchewan, Canada, to monitor matric suction and temperature changes with time. This paper presents and interprets the variations in matric suctions measured between the years 2000 and 2005 at the Torquay site. The readings in the field showed a clearly seasonal pattern of matric suction changes that bore a relationship to rainfall near the test sites. Relatively constant equilibrium matric suctions that ranged from 20 to 60 kPa throughout the years were measured under the driving lanes. Conversely, matric suctions under the side slopes were found to vary widely with time and depth, ranging from 100 to 1500 kPa over the years. The greatest variation in matric suction from one location to another location occurred during the month of April. The matric suctions showed low variability during June, whereas larger variations were observed from July to October.