banner

Frequently Asked Questions (FAQs)


Roundabout design features

Is the roundabout like a four-way stop?

Not really. The main similarity is that both roundabouts and four-way stop intersections do not have signals. The differences include: four-way stops yield to whoever arrives first, or the vehicle on the right, roundabouts yield to the left---like a right turn on red---because the circulating traffic comes from that direction. At four-way stops, each direction gets a turn in order. At roundabouts, each driver chooses a safe gap to enter and no driver "gets a turn."

Center Island

The circular central island around which traffic circulates; this island may be raised or flush with the roadway surface; a mountable/drivable truck apron may surround the center island; the truck apron accommodates the path of the rear left wheels of larger vehicles such as semi-tractor trailers, farm equipment, buses, etc.; the truck apron is generally constructed with a different material to discourage passenger vehicles from driving over it.

Circulatory Roadway/Circulating Lanes

The roadway around the central island on which circulating vehicles travel in a counterclockwise direction, entering and exiting only to the right.

Splitter Island

A raised or painted island separating entering and exiting traffic and placed within a leg of a roundabout; the splitter island also serves to deflect and slow entering traffic, as well as provides a refuge/safety zone for crossing pedestrians.

Yield Line

A broken line marked across the entry roadway where it meets the outer edge of the circulatory roadway and where vehicles wait, if necessary, for an acceptable gap to enter the circulating flow; if no traffic is in the roundabout, entering traffic may proceed without stopping.

Differences from rotaries, traffic circle, etc.

Isn't a roundabout just another form of an intersection?

Absolutely; and, just like stop signs and traffic signals it is important for drivers, pedestrians and cyclists to learn the rules for roundabouts.

Roundabouts, rotaries, traffic circles they're all the same, aren't they?

No. Other than sharing a circular shape, a modern roundabout operates much differently than other traffic circles, including rotaries. A modern roundabout requires entering traffic to yield the right-of-way to traffic already in the roundabout. This keeps the traffic in the roundabout constantly moving and prevents much of the gridlock that plagues rotaries. Modern roundabouts are also much smaller than rotaries and thus operate at safer, slower speeds. The design of a modern roundabout allows capacities comparable to signals but with generally a higher degree of safety.

Roundabouts-safety and efficiency

Benefit: fewer crashes and less severe crashes

Roundabouts benefit from good geometry, exhibiting only a fraction of the troublesome crash patterns typical of right-angle intersections. A typical four-legged intersection has 32 vehicle-to-vehicle conflict points and 24 vehicle-to-pedestrian conflict points. By comparison, a four-legged roundabout has only eight vehicle-to-vehicle conflict points and eight vehicle-to-pedestrian conflict points. This is an approximate 70 percent reduction in conflict points. In addition, since all vehicles are traveling in the same direction and at a lower speed in a roundabout, crashes are generally rear end or sideswipe in nature. Left-hand, right-angle (T-bone) and head-on crashes are virtually eliminated by a roundabout. The illustrations at the top of this page show the conflict points of a standard intersection and a typical roundabout. Studies by the Insurance Institute for Highway Safety show that roundabouts provide a:
    90 percent reduction in fatal crashes; 76 percent reduction in injury crashes; 30 to 40 percent reduction in pedestrian crashes; and 10 percent reduction in bicycle crashes

Why is Iowa installing roundabouts?

Roundabouts can offer a good solution to safety and capacity problems at intersections. At intersections where roundabouts have been installed in Iowa to replace existing intersections, crashes of all types have been reduced. Roundabouts can also offer high capacity at intersections without requiring the expense of constructing and maintaining a traffic signal.

Aren't traffic signals safer than roundabouts for pedestrians?

It depends on the amount of pedestrians and vehicles. In many cases, a roundabout can offer a safer environment for pedestrians than a traffic signal because the pedestrian crossing at a roundabout is reduced to two simple crossings of one-way traffic moving at slow speeds. A pedestrian crossing at a traffic signal still needs to contend with vehicles turning right or left on green, vehicles turning right on red, and vehicles running the red light. The latter of these potential conflicts occur at high speeds and often result in injuries or fatalities to pedestrians.

Benefit: pedestrians cross one direction of traffic at a time

Pedestrians need only cross one direction of traffic at a time at each roundabout approach, as compared with two-way and all-way stop-controlled intersections. The conflict locations between vehicles and pedestrians are generally not affected by the presence of a roundabout, although conflicting vehicles come from a more defined path at roundabouts. In addition, the speeds of motorists entering and exiting a roundabout are reduced with good design. As with other crossings that require acceptance of gaps in traffic flow, roundabouts still present visually-impaired pedestrians with unique challenges.

Are roundabouts safe near schools?

Over 30 roundabouts have been installed near schools in the United States. None have reported any significant problems.

Benefit: lower vehicle speeds

A standard stop sign or traffic signal controlled intersection always has at least one direction of traffic stopped. A roundabout uses yield-at-entry traffic control to eliminate stopping when it is not required.

Benefit: fewer vehicle delays

A standard stop sign or traffic signal controlled intersection always has at least one direction of traffic stopped. A roundabout uses yield-at-entry traffic control to eliminate stopping when it is not required.

Are roundabouts appropriate everywhere?

No. The choice of using a roundabout versus a traffic signal is a case-by-case decision. The Iowa Department of Transportation can assist in evaluating each candidate intersection to determine whether a roundabout or a traffic signal is more effective.

Benefit: less vehicle pollution

Vehicles entering a roundabout must yield at entry, but are not required to stop if the roundabout is clear. This eliminates some stop-and-go traffic associated with stop sign or traffic signal controlled intersections. This leads to fewer vehicles idling while stopped at an intersection.

Benefit: lower maintenance costs as compared to a traffic signal

A traffic signal requires electricity 24 hours a day. In addition, the signals need maintenance by field personnel for burned out lights, loop detector replacement, etc. A typical roundabout generally only needs electricity for streetlights at night and maintenance for landscaping, if included.

Benefit: increased landscaping opportunities

A standard intersection requires a large paved area to accommodate all the turning movements. A roundabout provides opportunity to landscape the center island, providing green space within the intersection

How to drive in a roundabout

I learned the rule as: "Yield to the Right." Is that correct in a roundabout?

At roundabouts, the traffic circulates counter-clockwise and moves toward vehicles at the yield line. Vehicle operators should always yield at the entry to circulating traffic. In practice, that means yield to traffic from the left, similar to the action that is necessary when entering a freeway or turning right at a red traffic light/signal.

Should I use my turn signal?

Yes. Especially when exiting the roundabout. This allows vehicles waiting to enter the roundabout to know your intentions.

Do I get a turn to go?

Roundabouts are not like four-way stops in the fact that there is not taking of turns among vehicle operators. Vehicle operators should enter the roundabout when there is a safe gap in the traffic flow.

Do I have to stop at the yield signs?

It depends on the amount of traffic already in the roundabout. When there is a lot of traffic, vehicle operators will probably have to stop at the yield sign and wait for a safe gap before proceeding. If a safe gap already exists, operators are not required to stop. However, vehicle operators should always slow down enough so they can stop, if necessary.

How large of a gap do I need?

This is a good-judgment decision based on the vehicle being driver, weather conditions and traffic flow. It is always the vehicle operator's responsibility to select a safe gap before crossing the yield line.

Is it okay to "let someone in?"

Vehicle operators in the roundabout may slow down so that the safe gap becomes more obvious to the driver wanting to enter the roundabout; however, they should not stop. Vehicle operators should not stop after crossing the yield line and are actually in the roundabout circle.

Does traffic approaching from one direction have priority over traffic approaching from another direction?

The only priority rule is that drivers inside the roundabout have the right-of-way over any driver entering the roundabout, regardless of approach direction. Every entrance has a yield sign for approach vehicles.

I know the rule is do not stop inside the roundabout. What should I do when someone else stops inside the roundabout?

Vehicle operators should always drive defensively and allow plenty of space between themselves and the vehicles ahead. If a driver becomes confused and stops their vehicle in the roundabout, be patient and wait for them to proceed. If a vehicle operator were to attempt to go around a confused driver, added confusion could result, possibly causing vehicle conflicts. So, it's in everyone's best interest to wait for these vehicles, and then continue through the roundabout.

What do I do when the driver in front of me is too timid at the yield line?

Be patient and wait for them to choose their safe gap. Try to avoid horn honking because it tends to cause less confident drivers to make mistakes.

While I'm waiting for my turn at the yield line I'm not sure what to do about the pedestrian crosswalks.

Vehicle operators should remain behind the pedestrian crosswalks until there is room for their entire vehicles to travel beyond the crosswalk.

What can we do about people who do not yield or speed?

First, practice defensive driving. Second, all drivers should try to set the right example by obeying the traffic signs, and others will learn and follow suit. All drivers should drive at a safe and consistent speed so other drivers can easily judge the traffic flow speed.

The roundabouts are nicely landscaped. Are there any special rules for using a roundabout during maintenance activities?

Drivers should be aware that routine landscape maintenance is common at roundabouts. Be courteous and drive cautiously when maintenance personnel are present.

Can I change lanes in the roundabout?

Vehicle operators should not change lanes once crossing the yield line and are in the circle portion of the roundabout. If there is a need to change lanes, vehicle operators should do so before reaching the yield line. A roundabout is like any other intersection. Get in the left lane to turn left and right lane to turn right.

Can I cross to the center island?

No.

I sometimes get trapped in the inside lane. What should I do?

Most multi-lane roundabouts are designed, signed and striped to minimize this problem by leading traffic to the exit points. If all else fails, simply go around once and try again.

I'm driving in a multi-lane roundabout. How do I choose which lane to enter and exit?

Multi-lane roundabouts should be approached the same way as any other intersection. To turn left, use the left-most lane and signal for a left turn. To turn right, use the right-most lane and signal for a right turn. In all situations, vehicle operators should pass counterclockwise around the central island. When preparing to exit, vehicle operators should turn on their right turn signals as soon as they pass the exit before the one that will be used.

What should I do when I'm in a roundabout when an emergency vehicle arrives?

If the roadway in the roundabout is wide enough, vehicle operators should pull as far to the right as possible and allow the emergency vehicle to pass. However, it is generally better to completely clear the intersection and pull off to the side past the roundabout.

Specific users

How do pedestrians use a roundabout?

Vehicle operators should remember to observe all the pedestrian crossing locations because pedestrians always have the right-of-way when they are in the crosswalks. Vehicle operators should never stop in the crosswalk while waiting for their turn at the yield line.

Pedestrians should always use the crosswalks; and make sure the vehicle operators see him/her before entering the crosswalk.

How do bicyclists use a roundabout?

Bicyclists have a legal right to ride on most roadways just like motorized traffic. Roundabouts are just like other intersections in that bicyclists may either follow the rules of the road and maintain travel on the roadway or use available paths and crosswalks to safely bypass the roundabout.

How do trucks use a roundabout?

Very large trucks can pass through roundabouts and will need both lanes to make wide turns. They can use the truck aprons (concrete area on the outside of the central islands) for additional space. Other drivers need to give trucks plenty of room. Expect trucks to use both lanes and don't get beside a truck in a roundabout because they may not be able to see smaller vehicles.

I drive a big truck and that roundabout looks awfully tight. Will I fit?

Yes. The roundabout has been designed specifically to accommodate large tractor-trailer units. As truck operators approach the roundabout, they should stay close to the left side of the entry. When passing through the roundabout, the trailer may track over the special apron around the central island - it was designed specifically for this purpose. When exiting, stay close to the left side of the exit.

At a multi-lane roundabout, tractor-trailer units may need to occupy the entire circulatory roadway to make the turn. Truck operators should signal their intention to do so in advance and claim both lanes on approach to the roundabout.

What about snow removal at roundabouts?

A number of communities in Iowa and other snowbelt states have installed roundabouts. All have indicated that while there is some initial adjustment in procedures for snowplow crews, roundabouts generally present no major problems for snow removal.