This is a road stud reflector, also known as a raised pavement marker or "cat's eye". These devices are installed on road surfaces to enhance visibility and guide drivers, particularly at night or in adverse weather conditions like fog or rain. The yellow color typically indicates the centerline or right-hand edge of the road, while the red reflectors on the opposite side may indicate a line that should not be crossed. The reflective material works by bouncing light from a vehicle's headlights directly back to the driver's eyes.