Roundabouts

What is a roundabout?

A modern roundabout is a circular intersection where drivers travel counterclockwise around a center island. There are not traffic signals or stop signs in a modern roundabout. Drivers entering the roundabout yield to traffic already in the roundabout, then enter the circulating roadway and exit at their desired street, so they function differently from older circular intersection types.

Studies by the Federal Highway Administration (FHWA) have found that roundabouts can increase traffic capacity by 30 to 50 percent compared to traditional intersections.

Types of circular intersections

There are more circular intersections than just roundabouts, and many differences between each type.

Traffic circles

Traffic circles, or rotaries, are much larger than modern roundabouts. In the graphic above, a traffic circle is shown in green, with a modern roundabout overlay shown in grey. Traffic circles often have stop signs or traffic signals where branches meet the circle. The Arc de Triomphe in Paris and Dupont Circle in Washington, DC, are examples of traffic circles.

Drivers enter the circle at a right angle like a typical perpendicular intersection and may not have to yield to traffic already in the circle. Traffic circles typically become congested if many vehicles enter at the same time.

Neighborhood traffic calming circles

Neighborhood traffic calming circles are much smaller than modern roundabouts and often replace stop signs at four way intersections. They are typically used in residential neighborhoods to slow traffic speeds and reduce accidents, but generally are not designed to accommodate larger vehicles. Many drivers often turn left in front of the circles, rather than turning around them as would be correct.

Modern roundabouts

Modern roundabouts are designed to accommodate vehicles of all sizes, including emergency vehicles, buses, and truck and trailer combinations. In a modern roundabout, drivers enter the intersection by navigating a gentle curve. Drivers yield at entry to traffic already in the roundabout, then proceed into the intersection and exit at their desired street.

A main feature of the modern roundabout is a raised central island. The circular shape is designed to control the direction of traffic and reduce speeds to 15 to 20 mph. It also reduces the likelihood of t-bone (right angle) or head-on collisions.

The central island of many roundabouts includes a truck apron (above), a raised section of concrete that acts as an extra lane for large vehicles. The back wheels of the oversize vehicle can ride up on the truck apron so the truck can easily complete the turn, while the raised portion of concrete discourages use by smaller vehicles.

In addition to the central island, roundabouts also feature triangular splitter islands designed to slow and direct traffic. The islands also provide a refuge for pedestrians. This means pedestrians can choose to cross one direction of traffic at a time and have a safe place to wait before crossing another direction of traffic.

Roundabout basics

Roundabouts are designed to make intersections safer and more efficient for drivers, pedestrians, and cyclists. There are two basic types of roundabouts: single-lane and multi-lane.

There are a few key things to remember about driving through roundabouts:

• Yield to drivers already in the roundabout (on the circulating roadway)
• Stay in your lane; do not change lanes
• Do not stop in the roundabout
• Avoid driving next to oversize vehicles

Want to learn more? We have a video available online:

• How to drive a roundabout - YouTube

You can also download our Rules of the Roundabout brochure in English and Spanish:

• Rules of the Roundabout (PDF 408KB)
• Español - Reglas de la Rotonda (PDF 379KB)

Pedestrians and bicycles in roundabouts

Modern roundabouts are designed to be safer than traditional intersections for people walking or using mobility assistance devices. Vehicles are moving at a slower rate of speed in roundabouts - typically 15 to 20 miles per hour (MPH).

Crosswalks (shown above in brown and white) are set further back from vehicle traffic, allowing more time for drivers to react to people in the roadway before merging into or exiting the roundabout. Triangular islands between lanes of vehicle traffic provide pedestrians moving through the roundabout a safe place to wait if they choose to cross only one direction of traffic at a time.

People using the crosswalk should look for approaching vehicle traffic, then move through the crosswalk to the triangular island. Before continuing, they should look for traffic entering or exiting the roundabout. When it is safe, they can continue through the crosswalk.

Bicyclists can choose to ride through the roundabout with traffic or walk their bicycles through the pedestrian crosswalks similar to a traditional intersection. Like people driving, bicyclists must obey the rules of the roundabout as they proceed through the intersection. Riders who choose to walk their bicycles may find that some roundabout designs have a ramp onto the sidewalk, making it easier for bicycles to transition from the roadway to the sidewalk.

Want to learn more? Watch a video about using a roundabout as a driver, pedestrian or bicyclist.

How to drive through a roundabout

How to drive through a roundabout depends on whether the roundabout is a single lane or multi-lane roundabout.

Driving single-lane roundabouts

When approaching a roundabout, there should be a yellow "roundabout ahead" warning sign with an advisory speed limit for the roundabout.

Slow down as you approach the roundabout, and watch for pedestrians in the crosswalk. Continue towards the roundabout and look to your left as you near the yield sign and dashed yield line at the entrance to the circulating roadway. Yield to traffic already in the circulating roadway. If there is no traffic in the roundabout, you may enter without yielding.

Once you see a gap in traffic, enter the circle and proceed to your exit. Make sure to stay in your lane as you navigate the roundabout, and look for pedestrians before you exit.

Watch a video about driving through a roundabout.

Driving multi-lane roundabouts

In a multi-lane roundabout, you will see two signs as you approach the intersection: the same yellow "roundabout ahead" warning sign and speed signs used for single-lane roundabouts, and a black and white "lane choice" sign. This second sign is to help you choose the appropriate lane for the direction you want to exit the roundabout.

You choose your lane in a multi-lane roundabout the same way you would in a traditional multi-lane intersection. Generally, to go straight or turn right, you would use the right lane. To go straight or turn left, you would use the left lane. Usually you can also make a U-turn from the left lane as well.

The graphics below show which turns can be made from each lane in a typical multi-lane roundabout. Arrows in yellow show movements that can be made from the right lane, and arrows in green show movements that can be made from the left lane.

Right turn

Straight

Left turn

U-turn

After selecting the appropriate lane, watch for pedestrians in the crosswalk as you approach the roundabout. At the dashed yield line, look to your left and yield to drivers already in the roundabout. It is important to remember that in a multi-lane roundabout, entering traffic must yield to both lanes of the circulating roadway. If there is no traffic in the roundabout, you may enter without yielding.

When there is a gap in traffic, merge into the roundabout in the correct lane and proceed to your exit. Look for pedestrians before exiting the roundabout.

Watch a video on how to drive through a roundabout.

Trucks, oversize vehicles, and vehicles with trailers in roundabouts

Roundabouts are designed to accommodate vehicles of all sizes, including emergency vehicles, buses, farm equipment, and semi-trucks with trailers.

Depending on the size and type of the roadway, the vehicle and/or its trailer may use specially designed truck aprons - raised sections of pavement around the central island that acts as a temporary lane for large vehicles. The back wheels of the large vehicle can ride up onto the apron due to its rolled curb, allowing the rear of the vehicle or trailer to off-track and successfully complete the turn. The truck apron is raised, and often a different color or material than the roadway, to discourage use by smaller vehicles and emphasize that it is not a normal travel lane.

In multi-lane roundabouts, large vehicles may straddle both lanes to make their turn. Because the rear of the vehicle or trailer is likely to off-track into the other lane while making a turn, other drivers should never drive next to large vehicles in a roundabout.

Benefits of roundabouts

Roundabouts have many important benefits over other intersection control types.

Improve safety

Studies have shown that roundabouts are safer than traditional stop sign or traffic signal controlled intersections.

Roundabouts reduced injury crashes by 75 percent at intersections where stop signs or traffic signals were previously used for traffic control, according to a study by the Insurance Institute for Highway Safety (IIHS). Studies by the IIHS and Federal Highway Administration (FHWA) have shown that roundabouts typically achieve:

• A 37 percent reduction in overall collisions
• A 75 percent reduction in injury collisions
• A 90 percent reduction in fatality collisions
• A 40 percent reduction in pedestrian collisions

There are several reasons why roundabouts help reduce the likelihood and severity of collisions:

• Low travel speeds. Drivers must slow down and yield to traffic before entering a roundabout. Speeds in the roundabout are typically between 15 and 20 miles per hour. The few collisions that occur in roundabouts are typically minor and cause few injuries since they are at such low speeds.
• No light to beat. Roundabouts are designed to promote a continuous, circular flow of traffic. Drivers need only yield to traffic before entering a roundabout; if there is no traffic in the roundabout, drivers are not required to stop. Because traffic is constantly flowing through the intersection, drivers do not have the incentive to speed up to try and "beat the light" as they might at an intersection with a traffic signal.
• One-way travel. Roads entering a roundabout are gently curved to direct drivers into the intersection and help them travel counterclockwise around the roundabout. The curved roads and one-way travel around the roundabout eliminate the possibility for "T-bone" and head-on collisions.

Reduce delay and improve traffic flow

Contrary to many peoples' perceptions, roundabouts actually move traffic through an intersection more quickly, and with less congestion on approaching roads. Roundabouts promote a continuous flow of traffic. Unlike intersections with traffic signals, drivers don’t have to wait for a green light at a roundabout to get through the intersection. Traffic is not required to stop – only yield – so the intersection can handle more traffic in the same amount of time.

Studies by Kansas State University measured traffic flow at intersections before and after conversion to roundabouts. In each case, installing a roundabout led to a 20 percent reduction in delays. Additional studies by the IIHS of intersections in three states, including Washington, found that roundabouts contributed to an 89 percent reduction in delays and 56 percent reduction in vehicle stops.

Lower cost

The cost difference between building a roundabout and building a traffic signal is pretty comparable. Where long-term costs are considered, roundabouts eliminate hardware, maintenance, and electrical costs associated with traffic signals, which can cost between $5,000 and $10,000 per year.

Less space

A roundabout may need more property within the actual intersection, but often take up less space on the streets approaching the roundabout. Because roundabouts can handle greater volumes of traffic more efficiently than traffic signals, where drivers may need to line up to wait for a green light, roundabouts usually require fewer lanes approaching the intersection.

Appropriate locations

Roundabouts are safe and efficient, but they may not be the ideal solution for every intersection. Several factors are evaluated when deciding to build a roundabout at a specific intersection. Engineers consider the following characteristics when determining the best solution for a particular intersection:

• Accident history. Data about the number of accidents, type of collision, speeds, and other contributing factors are analyzed.
• Intersection operation. The level of current and projected travel delay being experienced and backups on each leg of the intersection are examined.
• Types of vehicles using the intersection. It is important to look at all of the different kinds of vehicles that use the intersection. This is especially important for intersection frequently used by large trucks.
• Cost. This includes not only the basic costs of construction, but also social and economic costs, right-of-way (buying land) requirements, and long-term maintenance expenses.

Public opinion of roundabouts

Do you feel anxious at the thought of driving a roundabout? If so, you aren't alone. While many drivers get that "deer in the headlights" look initially, studies show that drivers tend to like roundabouts after using them.

After driving roundabouts, the number of people who favor them more than doubles. A survey on drivers' views of roundabouts before and after construction conducted by the Insurance Institute for Highway Safety (IIHS) illustrates public opinion. Before construction, the number of drivers in favor of roundabouts was only 31 percent, and those strongly opposed was 41 percent. After driving them, this shifted to 63 percent in favor and only 15 percent strongly opposed.

The reasons most cited for concern were fear of the unknown. People initially prefer traffic signals and stop signs until they realize roundabouts allow them through the intersection safely without having to stop. Other concerns about safety and possibly being confused about where to go also dissipate with use.