Source: WSDOT

Circulatory

roadway

Counterclockwise

circulation

Accessible

pedestrian

crossing

Apron

Splitter

island

Pavement

Markings

at Entry

Landscape

buffer

Bicycle lane

treatment

Central island

Sidewalk or

shared use path

Figure 1. Modern Roundabout Schematic

What is a Roundabout?

A roundabout is a type of circular intersection, but 

is quite unlike a neighborhood traffic circle or large 

rotary. Roundabouts have been proven safer and more 

efficient than other types of circular intersections.

Roundabouts have certain essential distinguishing features: 

1. Counterclockwise Flow. Traffic travels counterclockwise around a center island.

2. Entry Yield Control. Vehicles entering the roundabout 

yield to traffic already circulating.

3. Low Speed. Curvature that results in lower vehicle

speeds throughout the roundabout.

ROUNDABOUTS

& Rural Highways

For More Information

Jeffrey Shaw, P.E., PTOE, PTP

FHWA Office of Safety

2 0 2 . 7 3 8 . 7 7 9 3 or jeffrey.shaw@dot.gov

Hillary Isebrands, P.E., PhD

FHWA Resource Center

7 20. 5 45.4367 or hillary.isebrands@dot.gov

To learn more about roundabouts, please visit:

safety.fhwa.dot.gov

Publication number FHWA-SA-14-097 UPDATED jULY 2020

Cover image source: Washington State Department of Transportation (WSDOT)

State Hwy 55 at County Hwy KK

Calumet County, Wisconsin

The intersection of State Trunk Highway 55 (STH 55) and County 

Trunk Highway KK (CTH KK) was originally a two-way stopcontrolled intersection with a 55 mph posted speed limit on each 

approach. In a five-year period (2001-2005), 30 crashes occurred at 

the intersection resulting in 17 people injured and one person killed. 

The Wisconsin Department of Transportation (WisDOT) added 

intersection warning signs along STH 55 in advance of CTH KK 

and lowered the approach posted speed limits to 45 mph, but 

crashes continued to occur.

In 2006, WisDOT decided to reconstruct the intersection as 

a roundabout. They modified the design to account for the 

high-speed approaches by providing longer splitter islands 

and pavement markings, along with enhanced signing. These 

features help drivers recognize the roundabout well in advance, 

and to reduce their speed accordingly.

In the six-year period after construction, WisDOT reports there 

have been 11 total crashes resulting in one person injured and zero 

fatalities. These significant reductions in crashes made this project 

a success for WisDOT, and helped them move forward with other 

roundabouts along rural highways throughout the state.

FHWA identified roundabouts as a Proven Safety 

Countermeasure because of their ability to substantially 

reduce the types of crashes that result in injury or loss of life. 

Roundabouts are designed to improve safety for all users, 

including pedestrians and bicycles. They also provide significant 

operational benefits compared to conventional intersections.
Common Problems/Concerns Why Consider a Roundabout Real World Results*

Crashes at rural intersections often involve high 

speeds, which tend to result in severe injuries or 

fatalities. Roughly 1/3 of annual intersection fatalities in 

the U.S. occur along rural, two-lane highways.

Roundabouts are geometrically designed for 

drivers to negotiate the intersection at speeds in 

the range of 15-25 mph, regardless of the posted 

speed limits on approaches.

Roundabouts constructed at intersections along 

high-speed, two-lane rural highways reduced 

overall crashes by up to 68% and reduced injury 

crashes by up to 88%.

In many rural environments, drivers can miss a stop 

sign or traffic signal, leading to running through a 

stop sign or red light and resulting in an angle crash.

Because roundabouts require vehicles to yield and 

then navigate around a raised, circular island, the 

possibility of an angle crash is significantly reduced.

Roundabouts constructed at intersections along 

high-speed, two-lane rural highways eliminated 

83% of angle-type crashes.

For a driver turning left across oncoming traffic, it 

can sometimes be difficult to judge the speed of the 

approaching vehicle, resulting in misjudged gaps, 

and potentially severe crashes.

With roundabouts, there is no need to make a turn 

across opposing traffic. Entering vehicles yield to 

traffic already in the circle, and proceed when there 

is a safe gap.

There were 11 fatal crashes in the 5 year “before” 

period and ZERO fatal crashes in the 5 year “after” 

period at 19 roundabouts constructed along highspeed, two-lane rural highways in six different 

states (KS, MD, MN, OR, WI, and WA).

It doesn’t seem like people would slow down for a 

roundabout along rural highways. Motorists will just 

drive right into or over the roundabout because they 

won’t be able to slow down in time.

High-speed approaches to roundabouts include 

advance signing, pavement markings and raised 

channelization. With proper design, drivers adjust 

their speeds, slow on approach, and navigate the 

roundabout safely.

Researchers compared traffic speeds of approaches 

to roundabouts and stop-controlled intersections. 

At 100 feet before the yield or stop lines, the speed 

of traffic at the roundabouts was 2.5 mph lower 

than at the stop-controlled locations.

In the northeastern U.S., circles are being signalized 

or removed because they do not work. 

The old traffic circles and rotaries that are 

common in the northeastern U.S. are not modern 

roundabouts. 

Roundabouts are designed for slower speeds, 

require entering traffic to yield to vehicles already 

in the circular roadway, and to eliminate the need 

to weave or change lanes to exit. 

Why build something “different”, when all that is 

needed is either stop signs or a traffic signal?

Improvements like stop signs and signals, while 

very familiar, aren’t always the safest choice. With 

intersections representing about one-quarter of 

annual U.S. traffic fatalities and roughly half of 

all injury crashes, safer designs are needed that 

improve mobility while saving lives.

Since the late 1990s, an ever growing number of 

State DOTs and local road agencies are finding 

that roundabouts work in their jurisdictions. Their 

potential for saving lives is too significant to ignore.

* Sources:

Isebrands, H., S. Hallmark, N. Hawkins. “Effects of Approach Speed at Rural High-Speed Intersections “ Transportation Research Record: Journal of the Transportation Research Board, Volume 2402, Transportation Research Board, National Research Council, Washington, DC, 2014

Isebrands, H. and S. Hallmark. “Statistical Analysis and Development of a Crash Prediction Model for Roundabouts on High-Speed Rural Roadways” Transportation Research Record: Journal of the Transportation Research Board, Volume 2389, Transportation Research Board,

National Research Council, Washington, DC, 2012