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FHWA Home / Safety / Intersection / Intersection Safety

Intersection Safety

Long Version

FHWA logo. FHWA Office of Safety Logo: Safe Roads for a Safer Future, Investment in roadway safety saves lives.

Photograph of two cars wrecked in a crash.

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speaker notes:

This presentation is on the safety aspects of the modern roundabout. It covers the following topics:




slide 2

Terminology

Diagram indicates that roundabouts, rotaries, neighborhood traffic circles, and others are subsets of circular intersections.

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slide 3

What isn't a Modern Roundabout?

Three photos indicate that rotaries, traffic circles, and neighborhood circles are not modern roundabouts.

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Clockwise from upper left:



slide 4

What is a Modern Roundabout?

Photo depicts a roundabout in which traffic flows counter-clockwise around a circular center island, entering traffic yields, and approaches are channelized. A pathway is drawn to indicate the curving through lane and arrows indicate a counter-clockwise traffic movement around the circular center island.

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These four points are what differentiate a modern roundabout from other similar or related traffic control features. Use mouse clicks to bring up each point along with an illustration on the photograph:



slide 5

What is a Modern Roundabout?

Photo illustrating a high-speed rotary that is about 600 feet across.

Photo illustrating a high-speed rotary with a new roundabout and associated roadways being constructed in the center. The new center island is only about 120 to 250 feet across.


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slide 6

Roundabout History

Image of a timeline that indicates traffic circles and rotaries emerged in the U.S. from about 1900 to about 1940. From 1940 to about 1960, the British redesigned circular intersections and implemented a 'yield at entry' rule. In the 70s and 80s, what are considered modern roundabouts were widely used in the U.K., Europe, and Australia.

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Note: Click to build the slide as you talk about the history.



slide 7

Roundabouts in the U.S.

Pie chart shows that about 2 percent of roundabouts have three circulating lanes, 25 percent have two circulating lanes, and 73 percent have only one circulating lane.

Phie chart shows that 6 percent of roundabouts are set in rural locations, 58 percent are suburban, and 36 percent are urban.


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slide 8

Key Features


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slide 9

Yield Control

Two photos of yield signs posted at the entries to two roundabouts.


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slide 10

Circulatory Roadway

Two photos, one with arrows overlaid indicating the counterclockwise direction of traffic flow, the other of a one way sign.


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slide 11

Central Island

Photo of a roundabout with lines overlayed to highlight the curvature of the roadway around the circular center of the roundabout.


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slide 12

Splitter Island

Two photos of different shaped splitter islands.


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slide 13

Landscaping


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slide 14

Pedestrian Access

Two photos of brick paved pedestrian walkways set well back from the yield line and containing cutouts for curb access at both the sidewalk and splitter island segments of the crosswalk.


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slide 15

Truck Apron

Two photos of circular roundabout center islands with truck aprons.


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slide 16

Signing and Marking

Collage of signs indicating yield ahead, roundabout ahead, a yield sign, and speed limit 20 mph.


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slide 17

Signing and Marking

Two photos of signs in advance of complex roundabouts advising drivers of which lanes lead from the roundabout to which roadways, arterials, or highways.


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slide 18

Signing and Marking

Collage of photos showing a lane-use 'fishhook' diagram that can be used for multi-lane roundabouts, a dotted circulatory roadway delineation line, and a Yield line marking.


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As noted on Slide #9:



slide 19

Why a Roundabout?


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slide 20

Vehicle Conflict Points

Two diagrams, one of a roundabout and the other of a traditional intersection, showing the locations of vehicle conflict points. The roundabout diagram shows zero crossing points, 4 diverging points, and 4 converging points where conflicts may occur. The traditional intersection diagram shows 16 crossing points, 8 diverging points, and 8 converging points where conflicts may occur.


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slide 21

Vehicle-Pedestrian Conflict Points

Two diagrams, one of a roundabout and the other of a traditional intersection, showing the locations of pedestrian conflict points. The roundabout diagram shows 8 crossing points, and the traditional intersection diagram shows 16 crossing points where pedestrian conflicts may occur.

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slide 22

Type of Crashes

Two diagrams of typical 4-leg intersections, one showing an angle crash and the other showing a left turn crash due to failure to stop or yield.Diagram of a roundabout showing a sideswipe type crash from a vehicle failing to yield before entering the roundabout.


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slide 23

Study Results

Convert signalized intersection to roundabout.


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slide 24

Study Results

Convert two-way stop intersection to roundabout.


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slide 25

Older Drivers and Safety


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As human beings age, a number of our abilities begin to diminish. And many of them are critical to the driving task.

When comparing roundabouts to the conventional intersection design, most (if not all) of these factors are reduced, thereby making the roundabout a safer choice for older drivers.



slide 26

Older Drivers and Safety

Conventional Intersection Roundabout
High speeds Low speeds
Little response time
Situation changes slowly/More PRT
High energy crashes
Low energy crashes
Unforgiving environment
Forgiving environment
High severity crashes
Low severity crashes
Complexity Easier to judge gaps
Wide visual scans
Narrow visual scans


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This table illustrates the differences between conventional intersections and roundabouts. While the focus here is on older drivers in particular, it should always be noted that what is good for older drivers is almost always good for all categories of drivers.



slide 27

Reduce Congestion and Pollution

Photo of a vehicle yielding prior to entering a roundabout.

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slide 28

Save Money

Photo of a signal equipment box with a red bar across the front indicating 'no signal equipment box.'

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Frequently, roundabouts can save a jurisdiction money because:



slide 29

Complement Community Values

Photo of a landscaped roundabout replete with palm trees, flowers, and a fountain in the center island.

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slide 30

Special Considerations

Two photos, one of a bicyclist traveling in the right lane of a roundabout, the other of a pedestrian crossing a street at a well-marked pedestrian crosswalk.

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slide 31

Multi-Lane Roundabouts

Photo of a complex roundabout with four roadways converging to create a two-lane roundabout.

Photo of a very complex double roundabout where six roadways converge to create a two-lane roundabout adjacent to a three-lane roundabout. The roundabouts separated by a separator island.

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slide 32

Mini-Roundabouts

Two photos of small roundabouts, one that has a raised circular center island, the other with a circular center island area painted on the roadway.

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slide 33

Rural Roundabouts

Two photos of rural roundabouts. One photo shows the juncture of 4 roadways at the roundabout, the other shows a T-intersection with a roundabout at the junction. Both contain splitter islands.

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slide 34

Right-of-Way Requirements

Two 'before' photos of traditional intersections prior to having roundabouts installed, one in a neighborhood the other in an urban center.Two 'after' photos showing the layout of urban and suburban intersections after the application of roundabouts.


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slide 35

Where to Consider Roundabouts


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slide 36

Roundabouts in Corridors

Aerial photo of a corridor containing three consecutive roundabouts.

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slide 37

Roundabouts in Interchanges

Two photos of roundabouts at highway interchanges.

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slide 38

Roundabouts and Rail Crossings

Three photos showing roundabouts where train tracks traverse the circular center island.


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slide 39

Roundabouts and Schools

Aerial photo depicting two roundabouts on a roadway adjacent to a school.

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slide 40

Roundabouts and Driveways

Aerial photo of a neighborhood roundabout characterized by driveways on the adjacent roads leading into the roundabout.

Photo of a neighborhood roundabout with driveways letting out into the roundabout.


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slide 41

Issues to Review


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slide 42

Roundabout Resistance

Graph shows about 65 percent of respondents in a public opinion poll about roundabouts felt negative or very negative, whereas after construction about 70 percent of respondents felt positive or very positive about roundabouts.

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slide 43

Roundabout Resistance

Graph shows that the most common reason agencies have not built roundabouts is they are not sure if drivers will get used to them followed by uncertainty as to whether they work efficiently followed by uncertainty as to whether they are safe. Lesser concerns include liability issues and that roundabouts are not part of the AASHTO Guides.

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slide 44

Keys to Success

Photo of a front lawn with a sign displayed that says 'No Roundabouts.'

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slide 45

Roundabout Resources

Colage of cover art from roundabout resource documents.

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slide 46

For More Information


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Page last modified on May 2, 2017
Safe Roads for a Safer Future - Investment in roadway safety saves lives
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000