The effect of seasonal variations in field temperature on the shear strength of recycled asphalt shingles (RAS) improved by mixing with bottom ash (BA) was evaluated for their use as structural fill material in highway embankments. Typical field temperatures ranging from 5°C to 35°C were induced to compacted mixtures of RAS:BA. An increase in temperature reduced the shear strength of compacted mixtures of RAS:BA, and therefore temperature effects should be taken into consideration in design. The friction angle of compacted RAS:BA mixtures, however, remained within the range suitable for stability of embankment fills. Thermal cycling induced thermal preloading to the mixtures containing RAS; this preloading in turn increased shear strength. From these results, to achieve optimum engineering behavior, construction of highway embankments made with granular materials containing RAS is recommended during warm seasons. The use of RAS in high-volume structural fill applications can contribute to more sustainable roadway infrastructure.