Roundabouts in Cities: Skylines II work best when the circle is big enough for its traffic, entries are spread evenly, and the ring has no extra junctions inside it. The same technique works on regular, sunken and elevated roads — and even rail.
Roundabouts are the simplest traffic fix in Cities: Skylines II, when they’re built right. Built wrong, they’re a traffic jam with a circle in the middle. This guide expands the two-minute video into a checklist: how to build them on any road, and how to tell whether a junction needs one at all.
Ready-made or your own?
The game ships with ready-made roundabouts in several sizes. They’re fine for a quick fix. The video shows how to build your own instead, which works with sunken, regular and elevated roads, and even rail, and gives you full control over size, lanes and height.
What makes a roundabout flow
- Size matches traffic. Tiny rings fill instantly. A busy junction needs a ring large enough that cars can merge without stopping.
- Even entries. Spread the connecting roads around the circle. Two entries right next to each other force cars to merge and exit in the same few metres.
- Nothing inside the ring. Extra junctions, driveways or bus stops on the circle break the flow.
- One height. Keep the whole ring at the same elevation.
- Exits as wide as entries. A two-lane approach that leaves on a one-lane exit backs up into the ring.
Building it
- Clear the junction area. Leave more room than you think you need.
- Draw the ring as one closed circle. The video shows how to get a clean, even curve with any road type.
- Connect the approach roads at evenly spaced points around the circle.
- Run the simulation and watch the traffic overlay for a full in-game day, including rush hour.
One lane or two?
Start with one lane. A single-lane ring is easy for the simulation: everyone enters, drives, exits. A two-lane ring only helps when lane use is controlled with lane connectors (the Traffic mod), otherwise cars weave inside the circle and the extra lane causes more trouble than it solves.
On sunken and elevated roads
The technique doesn’t change: set the elevation first (see elevated roads and sunken roads) and build the whole ring at that height. Two combinations work especially well:
- A ground-level roundabout above a sunken main road. Through-traffic passes underneath; only turning traffic uses the ring.
- An elevated roundabout over a railway or highway, connecting both sides without a level crossing.
When not to use one
- Very unequal flows. A highway exit pouring into one direction often needs a dedicated slip lane or a signalised junction instead.
- Pedestrian-heavy centres. Roundabouts are hard to cross on foot. In a station square, signals or a pedestrian zone work better.
- Japanese-style builds. Japan has very few roundabouts; most junctions are signalised crossroads. If authenticity matters more than throughput, use signals. The Japanese cities guide has more on that.
Common problems
Traffic stops at the entries. The ring is full. Enlarge it, or take the busiest turn out of it with a bypass lane.
Cars change lanes inside the ring. Two lanes without lane rules. Go back to one lane or set lane connections.
Queues on one approach only. Flows are unequal. Give that approach a slip lane for its main turning movement.
These cases are what the Traffic Surgery series is for. Send in your junction if it’s one of them.
FAQ
Why does traffic still jam at my roundabout?
Usually the ring is too small, entries sit too close together, or one direction carries most of the traffic. Enlarge the circle, spread the entries or add a bypass lane for the dominant turn.
Can I build a roundabout on an elevated road?
Yes. The same technique works on elevated and sunken roads — set the elevation before drawing and keep the whole ring at one height.
One-lane or two-lane ring?
Start with one lane; a two-lane ring only helps when lane use is controlled, otherwise cars weave inside the circle.
Does Cities: Skylines II have built-in roundabouts?
Yes, there are ready-made roundabouts in several sizes. Building your own gives you control over size, lanes and elevation, and works with any road type.
Are roundabouts realistic in a Japanese city?
Not really — Japan has very few. Signalised crossroads and grade separation look more authentic, though a roundabout can still be the right fix for a busy game junction.
