Traffic and tunnels

[Bighnry 2]

Hey Simtropolis, so I'm trying to create a big city and I had an idea to use a central roundabout that would extend to an exterior avenue via a tunnel network of avenues. Working okay so far and is defintely maximizes denisty as im stting at 195k population with about 15%-20% map not used and most of my buildings sitting at level 2 density. 

However traffic is a huge issue! So here are some screenshots, any feedback or comments would help. 

 

[Rufus Honker IV 100]

I like the idea of a roundabout.  I've worked on several cities with two intersecting avenues in the center, a roundabout at the intersection would be interesting.

[Trooth 22]

My biggest lessons learned from traffic is to avoid having anything going on at the entrance/exit to the city as that alone can cause severe issues.  Avoid 4 way stops and just use 3 way stops as much as possible.  Use the park and rides.  Don't build along the avenues, build on the side streets.  You want to avoid people going into or leaving a building from the avenue.  Pretty much avoid anything that would cause a car to stop along the Avenue.  After that, you want to consider where things are grouped.  If you have all your people living in the SE of the map and all of the industry is in the NW of the map, you are going to have a lot of traffic all over, whereas if you keep citizens and industry both on one side, you can filter that traffic down the edge of the map and not impact the rest of the city with traffic congestion.  Beyond that, high density = congestion.  Don't make the mistake of throwing in any types of tourism, that can crush a dense city with gridlock traffic once the taxis and such come in.

[Robotica 36]

Just my 2 cents.... Now forgive me if you have done some of these already, but it's hard to tell from your pics... First off, and obviously, make sure you have a good, functioning mass transit system in place. Make sure that whaever transit system you have in this tile you also have in all the other tiles in the region as well. Also make sure that you are using ALL of the transit options, not just one of two of them. As mentioned above though, avenue placement and connections is key. Also having good intersections is quite helpful but isn't so effective without one way roads.  I just about finished a city this morning that is a tourism, gambling city with around 300k citizens and all HD buildings. The traffic is massive at certain points of the day and honestly I don't think there is much you can do about rush hour traffic, but following the tips that Trooth mentioned above, I am able to have the city manage the traffic fairly well. Really it's all about placement. Making sure that the areas where congestion does occur doesn't effectively destroy your city. For example in my tourist gambling city I have the whole area sectioned off to where all the traffic it makes is totally away from all the jobs, industry and services, so when traffic get's hectic during rush hour the city can still function properly. Sims don't loose their jobs, and freight can still get shipped around.

 

If you do something like place the heart of the traffic at the center of your town (pretty much like in your pictures I believe) you are going to have issues because the traffic has to filter out through your whole city, rather than being forced to be in cetain area. This is really something you learn more or less from practice and figuring things out from experience. Best of luck to you, there are tons of tips online about combating traffic.