Interactive Roundabout Simulator

Watch the physics of traffic flow, learn the right-of-way rules, and take the wheel yourself to test your driving skills.

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Exits Made
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Yields Given
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Near Misses
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Safety Score
Watch how traffic flows through the roundabout, then press "Drive It" to take the wheel!
WATCH MODE
3 cars circulating
Traffic Density
⇧ Accelerate   ⇦⇨ Steer   ⇩ Brake   — or use the D-pad above
The 5 Golden Rules of Roundabouts
1
Yield at Entry
Always give way to traffic already IN the roundabout. They have right of way — you wait at the dashed yield line until there is a gap.
2
Go Counterclockwise
Traffic flows counterclockwise (in North America). In the UK and Australia, it flows clockwise. Never go against the flow.
3
No Stopping
Once inside, keep moving at a safe, consistent speed. Stopping inside a roundabout causes congestion and accidents.
4
Signal Your Exit
Signal RIGHT as you pass the exit before the one you want. This tells others you are leaving. Signal LEFT if continuing past an exit.
5
Slow, Don't Stop
Approaching cars must slow and yield — but roundabouts are designed so gaps occur naturally. Rarely do you come to a complete stop.

How Roundabouts Work: The Physics and Rules of Circular Intersections

For many drivers, encountering a modern roundabout for the first time can be a confusing and slightly intimidating experience. Unlike traditional intersections governed by strict red and green traffic lights, roundabouts rely entirely on continuous fluid motion, geometry, and the universal rule of yielding. However, despite their initial learning curve, civil engineers and city planners across the globe are rapidly replacing traditional intersections with roundabouts. Why? Because the math and physics behind them prove they are significantly safer, vastly more efficient, and better for the environment.

Our free interactive Roundabout Simulator allows you to visually understand the mechanics of circular traffic flow from a safe, top-down perspective before taking the wheel yourself.

The Physics of Safety: Why Roundabouts Prevent Fatalities

The primary reason traffic engineers love roundabouts comes down to basic physics, specifically, kinetic energy and vector angles. At a traditional 4-way traffic light, vehicles often travel at high speeds (40 to 60 mph) in straight lines. When a driver runs a red light or makes an unprotected left turn, the resulting collisions are either head-on or perpendicular "T-bone" crashes. These high-speed, direct-impact angles transfer massive amounts of kinetic energy directly into the passenger cabins, resulting in severe injuries and fatalities.

Roundabouts completely eliminate these dangerous vectors:

  • Deflection and Centrifugal Force: The physical geometry of a roundabout forces every entering vehicle to curve to the right. To navigate this curve without losing traction due to centrifugal force, drivers are naturally forced to reduce their speed to 15-25 mph. At these significantly lower speeds, the severity of any potential collision is drastically reduced.
  • Glancing Blows vs. T-Bones: Because all traffic in a North American roundabout is flowing in the exact same counterclockwise direction, head-on collisions are physically impossible. If a crash does occur, it is almost always a low-speed sideswipe or a rear-end collision angles that result in minor vehicle damage rather than serious bodily injury.
  • The Statistics: According to the Federal Highway Administration (FHWA), converting a traditional traffic signal intersection into a roundabout reduces severe injury and fatal crashes by a staggering 78 to 82%.

The Fluid Dynamics of Traffic Flow

Beyond safety, roundabouts solve a major problem in traffic engineering: congestion. Traffic acts very much like a fluid moving through a pipe. When you install a red light, you are completely closing a valve, forcing the fluid (cars) to come to a dead stop, even if the intersecting road is completely empty. This causes massive delays and wastes millions of gallons of fuel through prolonged engine idling.

Roundabouts operate on the principle of yield-at-entry. Drivers approaching the circle do not face a stop sign or a red light; they face a dashed yield line. They only stop if there is an immediate conflict with a vehicle already circulating inside the ring. Because traffic is continuously moving and filtering into natural gaps, a roundabout can handle 30% to 50% more vehicles per hour than a traffic light. By eliminating the dead-stop requirement, roundabouts keep the "fluid" of traffic flowing smoothly, saving time and significantly reducing greenhouse gas emissions.

Mastering the Visual Elements of a Roundabout

If you switch our simulator into "Annotated View," you will notice several specific design features that make the system work:

  • The Splitter Islands: These are the raised, triangular concrete islands located at every entrance and exit. They serve two vital purposes: they physically deflect entering vehicles to the right (slowing them down), and they provide a safe refuge halfway across the road for pedestrians using the crosswalks.
  • The Yield Line: The dashed line at the entrance. This is the absolute most important rule of the roundabout: Traffic inside the circle ALWAYS has the right of way. You must yield to vehicles already circulating before crossing this dashed line.
  • The Truck Apron: The slightly raised, often reddish-colored inner ring surrounding the central island. Roundabouts are compact by design, making it difficult for massive semi-trucks or fire engines to make the tight turn. The truck apron is specifically built to support the rear wheels of large commercial vehicles, allowing them to hop the curb safely without damaging the landscaping. Passenger cars should never drive on the truck apron.

By understanding the geometry, physics, and simple yielding rules behind these circular intersections, you can navigate them with absolute confidence. Use our simulator to practice timing your entries, signaling your exits, and keeping the traffic flowing!