[2021] Traffic ruins this game

I suggest you check out these guides. Traffic isn't broken at all and can be fixed without mods (mods just give you more options to micromanage things), but you'll need to get rid of the assumption that it works like real life. In game all drivers are the most patient people ever and don't care about being stuck in a loooong que. They just pick the fastest route as if there was no other traffic and then go. They only change lanes when they need to.

How to traffic
Beginner's guide to traffic

And a little picture of how the AI uses lanes on similar, but slightly different roads. Switching between amount of lanes is really handy to get more lanes used.
https://i.imgur.com/hNsG2JU.jpg