Where does sand and gravel accumulate on a paved road with two lanes?

Explanation:

On a paved road with two lanes, the part of the road that will accumulate a greater amount of sand and gravel is typically along the edge of the road. This occurs because the action of vehicles tends to push debris towards the sides of the road as they travel predominantly in the tire tracks. Over time, this can lead to a noticeable accumulation of sand and gravel primarily along the road edges where the force of the moving vehicles does not displace these materials as much.

It is in contrast to the centre of the road or the right and left tire tracks, where the constant passage of vehicles would more frequently displace or kick up any debris, preventing significant accumulation in these areas.

This dynamic is somewhat analogous to the deposition of sediments in marine environments, where different materials are deposited at varying distances from the shore based on factors such as particle size and transport energy, resulting in a gradational boundary.