What is a roundabout?
A roundabout is a form of intersection control that provides safe and efficient traffic flow. It operates with yield control at the entry points, and gives priority to vehicles within the roundabout.
Why build a roundabout instead of installing a traffic signal (stop light)?
Roundabouts move traffic safely and efficiently through an intersection because of slower speeds, fewer conflict points and easy decision-making. Studies show that roundabouts provide a 90 percent reduction in fatal cashes, a 75 percent reduction in injury crashes, a 30-40 percent reduction in pedestrian crashes, and a 10 percent reduction in bicycle crashes.
Slower vehicle speeds (under 25 mph) mean drivers have more time to judge and react to other vehicles and pedestrians. Slower speeds make it easier to use for older and novice drivers, reduce the severity of accidents and help to protect pedestrians.
Roundabouts provide for efficient traffic flow because traffic is always on the move with less delay. There is a 30-50 percent increase in traffic capacity.
Other benefits of roundabouts include:
- Reduces in pollution and fuel use
- Reduces noise due to fewer stops and starts
- Eliminates signal equipment installation and repair
- Provides traffic calming
- Improves visual quality and character through aesthetic landscaping
What is the difference between a "traffic circle" and a roundabout?
Roundabouts are different from traffic circles in that traffic circles can involve stop signs, stop signals, or no control at all; traffic circles can be very large, operate at higher speeds and confusing to navigate, often requiring motorists to move from one lane to another.
Some traffic circles still exist (Belleville Square); however, safety and operational problems caused many of them to fall out of favor in the 1950s and 1960s.
Roundabouts are not traffic circles. Roundabouts follow a yield at entry rule, which requires approaching vehicles to wait for a gap in the circulating traffic before entering the roundabout. Roundabouts involve low speeds for traffic entering and driving through the roundabout; they use deflection to slow entering traffic and enhance safety. Vehicles in the roundabout have the right of way.
Another distinguishing difference between traffic circles and roundabouts is that roundabouts have a smaller diameter than most traffic circles, resulting in safer conditions and lower speeds. Vehicles can enter modern roundabouts much easier than traffic circles due to flared approaches, entry angles, slower speeds on the circulating roadway and the fact that vehicles entering roundabouts always yield to circulating traffic.
Entering a roundabout is as easy as making a right hand turn onto a one-way street.
Why roundabouts?
The geometry of a roundabout is designed so all motorists have to slow down.
Properly planned roundabouts are designed using rigorous standards based on specific turning volumes. Traffic circles are typically sized based on land availability, location, and design vehicle size.
Many of us have experience with a large, old style traffic circle (also called rotaries in some locations). The Du Pont Circle in Washington D.C. for example is a traffic circle, not a roundabout. Traffic circles are large in diameter, have high circulating speeds and can require some merging and weaving between lanes to exit. Traffic circles exhibit poor operation and high crash rates (Belleville Square is smaller and exhibits a better safety record, but is still a traffic circle, not a roundabout). Driving through traffic circles can be unnerving to the uninitiated driver. In some instances driving through traffic circles can be unnerving to any driver! People unfamiliar with the modern roundabouts often assume they cause similar problems since they are circular too. However, the yield at entry rule eliminates the “How do I drive this?” confusion.
Here is a brief history about traffic circles and modern roundabouts. In 1966, research in Great Britain led to a yield-at-entry rule. The yield-at-entry rule ended a locking problem in the modern roundabout, improved capacity, reduced crashes and created a complete change in philosophy of roundabout designed and operation.
In the mid-1970’s, research continued and engineers came up with another variable that introduced a revised design that recommended a curved vehicle path or deflection be added to prevent vehicles from taking too straight a path into the intersection.
By 1984, the modern roundabout came into being with three principal feature: yield to the traffic in the circle, deflection at entry and low design speed, according to roundabout studies in Kansas by E.R. Russel, G. Luttrell and M. Rys.
Wouldn't a traffic signal be safer than a roundabout?
Research from the Insurance Institute for Highway Safety and Maryland State Highways shows far fewer crashes occur at intersections with roundabouts than at intersections with signals or stop signs. Roundabouts are substantially safer than intersections controlled by stop signs, traffic signals or traffic circles. The majority of U.S. roundabouts have substantial safety performance because of their small diameter (compared to traffic circles), slower circulating speeds, flared approach and deflection, and yield control entrances.
Considering the massive costs to society related to traffic injuries and deaths, this is an extremely important benefit associated with roundabouts.
Couldn't a traffic signal handle higher traffic volumes better than a roundabout?
Many people do not realize how many vehicles can be processed at a properly designed roundabout intersection. In most situations, a roundabout can handle higher traffic volumes with less delay than traffic signals.
A single-lane roundabout can handle up to 2500 vehicles an hour. It would take two travel lanes and usually left and right turn lanes in each direction to match that capacity. In other words, a single-lane roundabout will handle the same capacity as other larger intersections.
Will a roundabout cost more than a traffic signal?
In some situations, modern roundabouts require more right-of-way at intersections than traffic signals, resulting in higher initial costs. However, in other cases, traffic signals require numerous lanes and lengthy turn lanes (for storage) to effectively move traffic through the intersection. In these situations, traffic signals may require more total right-of-way than roundabouts. (The O’Fallon roundabout requires very little new right-of-way.)
Additionally, roundabouts often solve traffic congestion problems without requiring road segments to be widened between intersections (known as the "wide nodes, narrow roads" philosophy) resulting in a net cost savings.
Another factor worth consideration is costs associated with crashes. Because they result in far fewer injury and fatal crashes than traffic signals, roundabouts produce lower long-term costs to society as a result of these crashes. Also, roundabouts do not require as much maintenance as signals and only require electricity for lighting at night. These factors result in long-term cost savings. Considering all of these items, roundabouts may cost more than traffic signals initially but are far less expensive in the long run.
Roundabouts might work in other locations, but can they work with our aggressive drivers?
Aggressive driving affects other motorists regardless of what kind of traffic controls are in place. Aggressive drivers are less of a safety threat when intersections are controlled by roundabouts than traffic signals and stop signs because (1) the potential for head-on and broadside crashes is almost completely eliminated with roundabouts and (2) speeds are lower. Roundabouts have been implemented with success throughout the world and U.S. Many of these locations have drivers that are aggressive, and roundabouts have worked well.
Aren't roundabouts confusing?
Roundabouts are different from traffic signals and will require drivers to learn how they operate. Experience in the U.S. has shown that motorists quickly adapt to this new type of intersection. Perhaps the newest illustrations of this are in Vail and Avon, Colorado, the location of numerous high-capacity roundabouts. Both of these cities are major tourist destinations with many thousands of first-time roundabout drivers using the roundabout intersections each year. Despite large number of drivers who have not driven roundabouts previously, these intersections work well and do not confuse motorists.
Will older drivers have a more difficult time negotiating roundabouts than traffic signals?
Two comprehensive studies of roundabouts in the U.S. have shown that the average age of drivers involved in crashes did not increase following replacement of traffic signals and stop signs with roundabouts. Although not conclusive, these results suggest that roundabouts do not pose a problem for older drivers.
Will the roundabout be unsafe for pedestrians and bicycles?
Auto-pedestrian crash rates are usually lower at roundabouts than at traffic signals. Those pedestrian injuries that do occur tend to be less serious due to the relatively low speeds encountered at roundabouts. Legitimate concerns have been raised regarding the ability of blind pedestrians to negotiate roundabouts, and this topic is under consideration within the U.S. transportation community. At intersections that are used by blind pedestrians, other countries such as the United Kingdom have implemented designed measures including signalized crosswalks with good success. Where appropriate, these measures will promote safe conditions for blind pedestrians.
Properly designed roundabouts also safely accommodate bicycles. Because vehicles are traveling at low speeds that are comparable to bicycle speeds, bicycles can negotiate a roundabout like motorized vehicles. Bicycles have two choices to negotiate a roundabout. The more avid and skilled bicyclists can merge into a traffic lane before the bike lane ends, ride close to the middle of the lane to prevent vehicles from passing, enter the roundabout after yielding to vehicles within the roundabout, circulate the roundabout being careful to watch for vehicles waiting to enter the roundabout and exit the roundabout as a normal vehicle would do. Bicyclists not wanting to enter traffic can use the sidewalk ramps where the bike lane ends, and proceed around the roundabout as a pedestrian on the sidewalk.
Won't roundabouts slow emergency vehicles? Can a fire truck safely negotiate the roundabout?
A roundabout is designed to be safely negotiated at about 20 mph. The average speed for roundabouts is between 15 and 25 miles an hour. The time lost negotiating the roundabout will only be a few seconds.
Roundabouts are carefully designed to accommodate emergency and large sized vehicles. Driver should behave in the same manner as they would on any other road if an emergency vehicle approaches: Yield to emergency vehicles in the roundabout. Exit, and if possible, pull over.
The O’Fallon roundabout has been designed to accommodate your largest fire-rescue ladder truck.
What about the location of rail crossings?
Installing a roundabout near a rail crossing needs to be evaluated carefully. The O’Fallon roundabout location was evaluated by Horner & Shifrin, and underwent a peer review by the Illinois Department of Transportation, citing no adverse safety effect. The proposed roundabout will actually significantly reduce the number of times traffic is stopped near the crossing. When the crossing is operational, drivers will be expected to follow the same procedure as they do today; don’t block the intersection, obey the warning gates.
There are a couple of benefits provided by the installation of a roundabout at this location: a u-turn movement will allow for drivers to select an alternate route, and the truck apron allows for bypass of backed up vehicles in the intersection.
What about the location of existing traffic signals? Will they affect the roundabout?
Just like railroad crossings, the location of traffic signals and other traffic control devices will have an effect on the operation of the roundabout. However, in the case of traffic signals, this effect can be a good one. In places like Towson, Maryland, a very high-volume urban multi-lane roundabout, the placement of traffic signals nearby actually helps to create artificial gaps in traffic approaching the roundabout. These gaps in traffic allow for the other high volume approaches to enter the roundabout. In this way, the roundabout functions much like a traffic signal.
What other cities have used roundabouts?
Roundabouts are growing in number throughout the United States; over 600 so far. Traffic Engineers and City Planners are discovering the benefits of roundabouts. An easy way to track the progress of roundabout construction is to search the internet for recent news articles and project websites.
| 
