What causes the shimmering of a hot road surface in the summer?

The shimmering effect observed on a hot road surface in the summer is primarily caused by the refraction of light. As the temperature of the road increases, the air just above it heats up, creating layers of air with varying densities. Light waves passing through these layers bend or refract, leading to the appearance of shimmering or wavering patterns. This phenomenon is an optical illusion, as the light is distorted by the heated air.