Even the most experienced snowplow drivers can have a problem with gravel drives or parking lots. Plowing gravel driveways and surfaces is actually more art than a science.
Gravel drives and surfaces offer a great many more obstacles than paved surfaces, and each area tends to be unique. There can be wheel ruts along a drive with a crown in the center. There can be potholes just about anywhere in the plowing path. There can also be areas where the driveway is tilted side to side, or up and down, which can cause the plow to dig into gravel or even the earth itself. And gravel drives, which are more often found in rural areas, tend to be curvier than paved drives.