In order to help with syncing across multiple clients from wherever we may all be in the world, it's now REQUIRED that everyone have their Population Density and Population Variety set to the very lowest setting. You can change this by pressing ESC on your keyboard, selecting Graphics and bringing the slider all the way to left on both of these.
Failure to do this results in AI traffic jams and often times horrible vehicle crashes and explosions.
If it appears that you are creating desync issues by not having this done, you may be kicked.