1. Module 1 A Nationally Emerging Practice
Roundabouts in the United States
Module A Nationally Emerging Practice
Introduction to Roundabouts
Welcome to Roundabouts in the United States. Module One, A Nationally Emerging Practice
Most people in the United States are unfamiliar with roundabout intersections. Today however, there is a growing volume of information on roundabouts that demonstrate how they have proven to be a safe and effective form of intersection design.
The whole concept of roundabouts may cause some people to say “we’ve never done it that way before, why should we change now” or “all we need is a signalized intersection to solve the problem.” Yet traffic engineering solutions have evolved over time and continue to evolve today.  

2. PHOTOGRAPHY SOURCE: David Plazack
Traffic Engineering
Traffic engineering principles are well rooted in history.
PHOTOGRAPHY SOURCE: David Plazack
Traffic engineering principles are well rooted in history. Records indicate that many engineering practices were utilized in ancient Rome. Techniques such as one-way streets, roadway guide signs, parking regulations, and prohibiting vehicles on certain roadways were all found on early roadway systems.
Sometime in the early 1800’s traffic management became an issue as urban populations gained in density. Pedestrian and horse traffic became such a problem in 18th century London that systems of traffic control devices began to appear, including colored lanterns and semaphore flags.
By the beginning of the 20th century the widespread usage of the automobile increased the need for safe traffic control as the increasing speed of traffic escalated safety issues regarding vehicle collisions and pedestrian safety.
Sometime in the early 1800’s traffic management became an issue.

3. Intersections
Intersections have always been a primary concern for transportation professionals.
Intersections have always been a primary concern for people involved in traffic engineering and planning.
Intersections are where people and vehicles cross paths with other people and vehicles going in a different direction.
Transportation professionals design intersections to promote safety and to function at acceptable Levels of Service.
As traffic volumes increase, the configuration of the intersection approaches can be modified to accommodate the increased traffic.
As traffic volumes increase, configuration of the intersection can be modified to accommodate traffic.

4. Intersection Traffic Control
Early forms of intersection traffic control required the presence of a human operator.
Traffic signals and pedestrian activated devices have become the preferred method to manage traffic through intersections.

5. Circular intersections
Circular intersections have been used in this country in the past.
PHOTOGRAPHY SOURCE: United States Geographic Survey
Dupont Circle, Washington DC
Circular intersections that require all motorists to travel in the same direction have been used in the US and other countries in the past. This solution improves safety for the motorists as it eliminates crossing maneuvers that commonly occur with many intersection designs.
This design was employed most often along the east coast of the US with circular intersections such as the Dupont Circle in Washington.
Transportation engineers found that this design often resulted in traffic congestion on the roadway and the use of circular intersections in the US was halted.

6. Roundabouts: An alternative
The roundabout is yield controlled, traffic flows with fewer stops.
PHOTOGRAPHY SOURCE: Lee Rodegerdts
As recently as the early 1990’s a new form of circular intersections have emerged. This has been based on the lessons that the British learned in the 1960’s where a yield control on the entry to the intersection rather than a stop condition resulted in a much safer and more efficient intersection. Because the roundabout is yield controlled, traffic flows more continuously with fewer stops, unlike a four-way intersection where two or more movements are always stopped. Besides the obvious advantages in time savings and level of service improvements, air quality also benefits when motorized traffic is kept in motion. The roundabout can be an effective solution for an intersection even when analysis indicates that installation of a traffic signal is warranted and unlike a signalized intersection, a roundabout does not require electricity to operate effectively 24 hours a day.
Air quality also benefits when motorized traffic is kept in motion.

7. Roundabout Rules of the Road
The rules for traveling through a roundabout are easily explained and will eventually be included in most state driver’s manuals.
As this sign begins to appear more frequently on the roadway system, we can also expect to start seeing it in our in our driver’s manual as well. The rules for traveling through a roundabout are easily explained and will eventually be included in most state driver’s manuals.
Special brochures are also produced to introduce these new additions to the roadway system to the general public.
Special brochures also introduce these new additions to the public.

8. The Future of the Modern Roundabout
As safety and environmental advantages become recognized, roundabouts will be adopted by transportation professionals just like other technological advances.
Photo: Maryland SHA
Science and technology advances, and new options evolve. Roundabouts provide an opportunity to manage traffic flows and provide many benefits over signalized intersections or stop controlled intersections when designed and located appropriately. Roadway systems of the future will use roundabout designs to transition the character of traffic flows, for instance from a rural to urban driving conditions or from business to residential areas. As the safety and environmental advantages become recognized, roundabout design will be adopted by transportation professionals just like other technological advances in the past.