U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
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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.
|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.|
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.
Figure 1. Modern Roundabout Schematic
Roundabouts have certain essential distinguishing features:
Jeffrey Shaw, P.E., PTOE, PTP
FHWA Office of Safety
708.283.3524 or firstname.lastname@example.org
Hillary Isebrands, P.E., PhD
FHWA Resource Center
720.963.3222 or email@example.com
To learn more about roundabouts, please visit:
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