A white diamond painted on the road typically indicates a reserved lane or a specific warning. It most commonly marks lanes reserved for certain types of vehicles, such as high-occupancy vehicles (HOV), buses, or bicycles. These lanes have restrictions on which vehicles can use them and are often enforced to improve traffic flow and safety. In some contexts, a white diamond on the road also serves as a warning that you are approaching a pedestrian crossing, especially where the crossing may be less visible to drivers due to obstructions or lighting conditions.

Summary of meanings:

• Reserved lanes for specific vehicles such as HOV (carpool), buses, or bicycles (marked with a white diamond).

• Approaching pedestrian crossing warning, particularly when the crossing is not highly visible.

The exact meaning can depend on the local road rules and signs accompanying the markings, but the two main uses are reserved lanes and pedestrian crossing warnings.