Widening my driveway
It looks from the photo like this is a crushed gravel drive that hasn't been &quot;refreshed&quot; in a few years.  I have a similar drive and I have &quot;eights with dust&quot; or #8 gravel delivered.  You can ask the materials company what they recommend but around here (Central Indiana USA) most gravel drives use this.
Crowning is not as important on a drive as it is on a public roadway but you may want to adjust the overall crown for the new width to help with drainage.
You also need to consider the base for the new section.  Eights are used as a top layer.  It's common to use &quot;threes&quot; or #3 crushed gravel for the base.  I'd apply the #3 on the new section and let it settle and be driven on for a few weeks.  Then apply a top layer of #8.