Gadriel's Cities: Skylines

Cims & Traffic

Traffic is the perennial problem of all city planners. Planning a city in Cities: Skylines is no different. If your city is beset by traffic jams and congestion, it will foster unhappiness, reduce productivity, and can even cause the city to fail. But if you master traffic, then your city—and its cims—can be happy and prosper. 
Pedestrians

First and foremost, cims love to walk. If your cims walk to the neighborhood store, rather than having to travel by car, it reduces traffic, which reduces road congestion. It also means fewer and smaller roads can be used, which reduces noise. 

So, be sure to have paths for pedestrians in residential areas leading to commercial areas, and from residential areas to industrial areas, and connecting residential areas. Look where pedestrians will cross roads, especially major roads, and consider pedestrian bridges so traffic can continue without stopping. Automatic Pedestrian Bridge Builder by kian.zarrin & Chamëleon TBN can be handy for building pedestrian bridges at intersections. 
Buses

Buses are the first form of mass transit available in Cities: Skylines. Buses have the advantage of being able to stop frequently. The disadvantage is that they can clog traffic, especially at bus stops. Consider using avenues with bus lanes. 

With the borough design, each borough has a bus line which circuits the beltway avenue. There are two stops on each of the four sides, or eight stops. The bus line always turns to the near corner (for right-side driving, all right turns, or clockwise). That way, the bus never crosses traffic lanes and stays in the bus lane. 

Adjacent boroughs have adjacent bus stops. Cims love to walk, so to transfer between bus lines or boroughs, the cims take a pedestrian bridge. In the video, note how few vehicles are on the avenue or residential roads, even though it is a high-density area.
​Rather than increasing the number of buses on a line, additional bus lines that circuit several boroughs, or the entire city, can be added. Again, try to keep buses turning to the near corner (for left-side driving, all left turns, or counter-clockwise). 
Managing Traffic

If the city is well-designed with proper road hierarchy, then most traffic problems should be minimal. In this city, note that each borough and industrial area has direct access to the highway through a highway roundabout. Each borough is circuited by a six-lane beltway avenue with bus lanes. And only a few residential roads intersect directly with the avenue. Pedestrian bridges cross the avenue wherever pedestrians need to cross the avenue or highway, obviating the need for crosswalks on high traffic roads. 

Priorities: Setting priorities for roads (shift) and roundabouts (ctrl-shift) with TM:PE, Traffic Manager: President Edition by LinuxFan et al. can help your cims navigate through the city more efficiently. 

Roundabouts: If a road entering a roundabout become congested, you could try setting the incoming road to allow traffic to "enter blocked junction." That way, they will push their way onto the roundabout. Allowing lane changes on highway roundabouts can also alleviate some of the problems. Then, if you set the speed limits on the outer lanes a bit slower, traffic will tend to use the inner lanes until they are ready to exit the roundabout. This evens out the traffic flow across lanes and allows new traffic to more easily merge on the outer lanes. If the highway is backing up, you can widen the approaching road to create an exit lane, widen the on ramp from one lane to two lanes, or increase the number of roundabout lanes.  

​Intersections: Sometimes, all it takes to fix traffic congestion is a timed traffic light. If one road has most of the traffic, then set the timer so that the traffic on that road clears before the light changes. If you note that most of the traffic is turning a specific direction, then you can set the lane turns to accommodate the need. With the borough design, the only place timed lights are usually needed are at entrances from the highway, and intersections of two avenues from adjacent boroughs. 

Collector Roads: If a collector road leading from the residential area is becoming congested, try setting the speed limit a bit lower in that area. Cims will look for the fastest way to their destination without considering traffic congestion, so if you lower the speed limit, they will consider taking another route. 

Distributor Roads: With roads leading to multiple train stations, trucks look for the fastest route, but are not aware of congestion, so they will tend to congregate on the shortest route. Sometimes, you can make the roads artificially longer with a switchback, but you can also just lower the speed limit on the congested road until the traffic flow is more evenly distributed. It doesn't actually slow the congested traffic, as congestion traffic may be barely crawling anyway. Indeed, a lower speed limit can make the traffic move faster!

Lane Connectors: Finally, if all that doesn't work, you can set lane connectors to direct traffic in a very specific way. 
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