I would like to create and save my own custom traffic pools to load for freeroam traffic. I really don't like the selection it picks when I include mods and the default one has gotten a bit stale. I know about spawning in individual cars and starting traffic but that is a bit time consuming.
If you don't want to waste time spawning individual vehicles you can spawn vehicle groups by using the world editor (Default key = F11, in game Location = Window > Gameplay > Vehicle Groups manager) though I have not explored other options.