Roundabouts

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What is a Roundabout?
A modern roundabout is a circular intersection where drivers travel counterclockwise around a center island. There are no traffic signals or stop signs in a modern roundabout. Drivers yield at entry to traffic in the roundabout and then enter the intersection and exit at their desired street.

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

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 or head-on collisions.

The central island of many roundabouts includes a truck apron, 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.

Elements of a roundabout are shown in the figure below:
Roundabout Features

Why are Roundabouts Being Considered?
Roundabouts offer a sensible solution to safety and capacity problems at some intersections. Each of the intersections was evaluated for the varying benefits that can be achieved through roundabout installation including: crash reduction, reduction in crash severity, operational efficiency, as well as location in order to take advantage of “gateway” and other aesthetic benefits that roundabouts provide. Several benefits of roundabouts are shown below: 

>Improve Safety
Based on a study by the Insurance Institute for Highway Safety, roundabouts have been shown to provide: 

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

There are several reasons why roundabouts help reduce the likelihood and severity of collisions including low travel speeds but, the primary reason for this is the reduction in vehicle-vehicle conflict points. As shown in the figure below, a traditional intersection has 32 conflict points as opposed to a roundabout which has only 8.

Vehicle Conflict Points - Roundabout Versus Conventional Intersection
Vehicle Conflict Points

Vehicle Pedestrian Conflict Points – Roundabout Versus Conventional Intersection
Pedestrian Conflist Points

Moreover, roundabouts are also more effective during power outages. Unlike traditional signalized intersections, which must be treated as a four-way stop or require police to direct traffic, roundabouts continue to work like normal.

>Reduce Congestion
Studies have shown that 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.

>Reduce Pollution and Fuel Use 

  • Fewer stops and hard accelerations, less time idling
  • Multiple approaches are able to enter roundabout simultaneously

>Complement Other Common Community Values 

  • Quieter operation
  • Functional and aesthetically pleasing:
    Center island allows for landscaping, fountains, and monuments to be installed
  • Less expensive to maintain than a traffic signal

How to Drive a Roundabout?
Driving roundabout merely requires the ability to perform a right-turn both entering and exiting. Below are some tips for driving through a roundabout: 

    1. Slow down. Obey traffic signs. 
    2. Yield to pedestrians and bicyclists. 
    3. Yield to traffic on your left already in the roundabout. 
    4. Enter the roundabout when there is a safe gap in traffic. 
    5. Keep your speed low within the roundabout. 
    6. As you approach your exit, turn on your right turn signal. 
    7. Yield to pedestrians and bicycles as you exit.

The following link is an instructional video that shows how to navigate through a roundabout: http://www.youtube.com/watch?v=XcK8sjzTlWI

The following link is an interactive website that graphically shows how to navigate through a roundabout:
http://www5.mississauga.ca/marketing/websites/sheridan/roundabouts3.html

Other Roundabout Links 
FHWA http://safety.fhwa.dot.gov/intersection/roundabouts/fhwasa08006/#key 
Roundabout myths http://www.slideshare.net/thecityalliance/fhwa-roundabout-presentation
Public opinion http://www.youtube.com/watch?v=zLMMGclhbEY
Trucks http://www.youtube.com/watch?v=0nVzsC2fOQw  
   

In the News
CNN - Carmel, Indiana http://www.youtube.com/watch?v=WaICdKez2jg

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