It also might explain why Apple has been seeding new map expansions to small groups of users, weeks before releasing them to everyone.

Because of data licensing restrictions, Apple likely can’t use traffic data derived from the old map in order to make the new one. So Apple might be seeding new map areas to get traffic information that it can feed back into the map for road prioritization.

And if you watch how the new map has been changing while Apple has been “testing” it, this seems to be what Apple is doing. As time goes on (and as Apple accumulates traffic information), more and more roads are upgraded to arterials: