Increase the AI traffic in Options > Settings > Display > Traffic Tab and move the sliders up for Airline traffic density and/or General aviation traffic density, until you have enough AI traffic to keep you going. Be prepared for a hit on your frame rates though. It might be a good idea to turn the sliders down or even off for Road Vehicles, Ships and Ferries and Leisure Boats which will give you back some of the lost frame rates cause by air traffic.

Mark