This is my personal traffic spawning file. It's geared towards realism and not every car in the game will spawn,
I've left out of a lot of hypercars and anything unrealistic like the Phantom Wedge, 
and certain cars I just think are ugly, like the Revolter. 

To intall, copy and paste file to:

mods > update > update.rpf > x64 > levels >  gta5

To prevent DLC cars from despawning, you will need this trainer:

https://www.gta5-mods.com/scripts/simple-trainer-for-gtav