how to remove or reduce the traffic?
Currently not really possible.
Jase Edit: AI is synced between clients rather than serverside, similar to GTA IV Multiplayer’s AI system. Density toggles in settings will affect you and others near receiving your traffic.
Disabling cars/peds in Simple Trainer, will affect you and other players nearby. But when other players are near by, you will get traffic from them unless they have done the same.