Why are gravel/stone driveways and parking areas considered an impervious surface?

Gravel/stone driveways and parking areas are generally considered to be impervious surfaces due to the compaction of the gravel/stone and the underlying soil by vehicular traffic.   In addition, over time, gravel/stone driveways and parking areas collect debris/dirt that is also compacted into the surface, making the surface more impermeable.   It is difficult for water to soak into a packed gravel/stone surface.   Like concrete or asphalt, compacted gravel/stone functions as a barrier to absorption and places a demand on the storm drainage infrastructure.