The current iteration of the goto traffic manager mod is the presidential edition, https://steamcommunity.com/sharedfiles/filedetails/?id=58342.... It has some features like the dynamic lane selection and an alternative AI model (I think) that help even without manual work. But yes, assigning lanes at intersections, planning the number of lanes accordingly to have onboard lanes and in general avoiding that traffic collides takes some manual work. It can be fun though. I did not notice the performance going down too much.

I play City Skylines only to tune my roads with that mod. It's awesome, but in general I think the game has some annoying flaws, like that bringing dead people to graveyard is like a logistical problem, the blocky zoning makes neighborhoods boring, buildings are never that big, etc.

In CS the only way I found to have even moderately decent traffic flow was to make absolutely every street a one-way street. I don't claim to understand why that helps, but it seems to.

The downside is you have to be very careful where you place your emergency services as you can easily get zones which are too far for firefighters to reach.

This is exactly why I quit playing as well.