Looks like regular old pea gravel.
Makes a nice crunching noise underneath your tires.
Back in the days before every community became so anal about paving everything, pea gravel was widely used for parking lots, alleys, driveways - it was cheap and made an "all-weather" surface (i.e. it didn't turn to mud when it rained, and it mostly kept dust down).
When it starts wearing thin? - bring in a couple more truck loads!
Sadly such an effective and low-tech approach is not even considered anymore.