The traffic simulation in Cities: Skylines is easily the most complex aspect of the game. Electricity jumps from building to building, water pipes are either full or not, and entertainment buildings boost every building nearby, but every last citizen, service vehicle, and cargo truck exists in the game and can struggle to reach its destination depending on all the traffic in the way.
This is why the game provides players with dozens of different road options, and even more road types join them in the various expansions. Managing traffic and avoiding jams takes a lot of time and brain power, so it helps to know how players can keep people moving as their cities continue to grow.
Keep an Eye on the Traffic View
One quick way to see where all the traffic is backing up is to check the traffic info view. The icon for this view is a picture of several cars. Just like a phone traffic app, green means that vehicles are moving at full speed while orange and red show where cars are having to slow down or stop. This view won't tell players what to do to fix traffic congestion, but it does show where players should focus their attention.
Make Use of Roundabouts
Roundabouts aren't common in the United States, but they can be very useful. A roundabout is an intersection where no one has to come to a complete stop. This can keep vehicles moving where a stoplight would make them sit and wait, but in exchange a roundabout takes up more space and traffic can still come to a halt within the roundabout depending on how busy the neighboring streets are.
Check for and Adjust Traffic Routes
Another useful info view is "Traffic Routes." The icon for this view looks like a left and right arrow. In this view, players can click on pedestrians and vehicles to see what route they want to take, and they can check roads to see how busy they are and what kind of vehicle is using them.
One more thing players can do in this view mode is inspect junctions and switch them between signs and stoplights. By default, wide-road intersections use stoplights, narrow-road intersections use signs, and highway intersections can't have stoplights.
Signs are the better choice when one road gets a lot less traffic, but if both roads have a lot of cars on them then lights are the best option. This view also lets players create their own roundabouts: simply build a circular road and make sure every intersection on it uses signs instead of lights.
Invest in Public Transportation
Buses, metros, trains, and other options in the transport tab can ease traffic congestion by encouraging citizens to avoid driving. Instead, they'll use public transportation and take up less space on the road. To see how much a given public transport line is helping, players can check the individual line menu for a number called "car trips saved." This indicates how many passengers who could have driven to their destination are using other ways of getting around.
Of course, it's also important to make these lines as efficient as possible. Bus lanes allow buses to reach their stops faster (plus the driver AI never seems to use every lane of a six-lane road), and circular routes with well-placed stops that overlap with other lines will get as many passengers as possible.
Players should also make sure a line has enough trains or buses, and they can adjust an individual line's budget to add more vehicles and move more passengers or cut down on vehicles and avoid filling the road with empty buses. Another option is to switch to a high-capacity bus or train type, either from the base game, from an expansion, or from a mod.
Create Cargo Depots
Cities: Skylines doesn't just track citizens and tourists. It also tracks cargo deliveries, including raw resources going to industrial zones and finished goods traveling from industrial zones to commercial zones. This traffic is especially bad since trucks are noisy and take up a lot of space.
Players can control truck movements by building cargo hubs that connect to railroad tracks, shipping lanes, or (with the Airports DLC) cargo airlines. This will let industrial zones ship goods to commercial zones without using the road system in between, and it lets both zones import and export their products while avoiding the highways.
Don't Make Everything High-Density
When players reach the Big Town milestone, they get the ability to create high-density commercial and residential zones. This is great for bringing in more jobs and more citizens, but high-density living conditions generate high-density traffic. Players should be prepared for the extra demands on the road system that high-density buildings create, and they may want to stick with low-density zones in some areas to avoid traffic jams.
Narrow Roads Have Their Place
Just like how players shouldn't upgrade to high-density zones in every location, they also shouldn't upgrade to medium and large roads as soon as they can afford to. Narrow roads have lower speed limits, which means they generate less noise pollution even when drivers use them often. This makes them ideal for residential neighborhoods, including high-density neighborhoods. The slow speed limit also encourages vehicles that need to pass through an area to find another route, because the driver AI checks both distance and speed limits when choosing the fastest path.
Another option is the strategic use of one-way roads. By preventing traffic from moving in both directions, players can lengthen vehicle routes and encourage them to avoid residential roads that would otherwise be convenient.
These benefits also apply to pedestrian and bike paths, assuming players have the right expansions. Strategic inconvenience allows players to encourage citizens to use other methods than driving, and to drive down the right roads.
Space Out Intersections
A big cause of traffic jams in Cities: Skylines is a series of intersections that come one after another. Vehicles will slow down at every intersection even if there are no lights and no cars are coming from another direction, and if there are lights they can end up stuck three intersections back.
To avoid this problem, players should combine some intersections together to create only one point where vehicles have to stop. They can also remove intersections and use back roads to reach the streets that used to be connected at both ends.
Give Every Neighborhood Multiple Entrances
To keep those intersections apart, players can limit the number of ways for vehicles to enter a neighborhood. This is especially useful for residential zones since vehicle traffic is a big source of noise pollution. However, to avoid traffic jams at the entrances to residential zones, make sure there's at least one way in on each side of the neighborhood. Densely populated neighborhoods may need extra routes.
Don't Zone Arterial Roads
An "arterial" road is one that gets a lot of traffic because it makes a lot of connections and leads directly to the highway. Traffic should be able to move quickly down these roads, and one thing that can stop traffic is vehicles coming in and out of the buildings that line the road. So while players may want to zone every available square to maximize their profits, doing so along arterial roads can create traffic snarls that make the whole neighborhood drop in service quality.
Keeping these roads clear of zoned buildings also gives players a place to put service buildings like police stations and medical clinics. Just make sure these buildings face the side roads to keep merging traffic to a minimum.
Wait a Few Minutes After a Fix
After players alter the road network, they should let the game run for a few minutes before deciding whether the fix worked or not. The cars that currently exist already have their routes planned out, and they won't adjust any more than necessary to reach their destination.
Instead, the real test is what happens when new vehicles spawn in and choose a route. These vehicles will take some time to reach their destinations, and meanwhile the existing vehicles will need some time to clear out. Don't get frustrated when nothing changes right away, just give it some time and let the game figure things out first.
Cities: Skylines is available now on PC, PS4, PS5, Switch, Xbox One, and Xbox Series X/S.