Easing Congestion
Modern roundabouts offer safer, greener solution
Traffic engineers are embracing a safer and greener solution to congested intersections. Modern roundabouts can improve traffic flow and dramatically reduce the risk of serious accidents, while offering environmental advantages.
What is a modern roundabout?
A modern roundabout is a one-way, circular intersection where traffic flows around a center island. It is designed to provide safe and efficient traffic flow through an intersection. The modern roundabout uses “yield at entry” and special geometry to calm traffic, dramatically reducing serious accidents over standard signalized intersections.
What makes it modern?
Traffic circles and rotaries do not necessarily offer the same safety and operational benefits of a modern roundabout. Modern roundabouts have key design features that set them apart from traffic circles and are much smaller in size than many of the traffic circles that were built 30-50 years ago. The two features that qualify an intersection as a modern roundabout – usually absent in traffic circles – are:
- Yield on Entry - Traffic entering the roundabout must yield to traffic already in the roundabout
- Deflection of Entering Traffic - Traffic entering the roundabout is deflected to the right to reduce the entering speed and to align the vehicle correctly with the roundabout
Why build a modern roundabout?
The Federal Highway Administration (FHWA) states that “building more well-designed roundabouts will result in fewer crashes and less delay than stop- and signal-controlled intersections.”
The FHWA has studied the benefits of modern roundabouts:
Be Safe
Modern roundabouts have the potential to reduce fatalities by 90 percent, reduce injury crashes by 76 percent and lower pedestrian crashes by 30 to 40 percent. Because the only movement allowed upon entry or exit from a roundabout is a right turn, the occurrence of crashes that result in injury is substantially reduced.
Be Green
Improved traffic flow at a modern roundabout means fewer vehicles are idling at a congested intersection. Breathe easier knowing that improved traffic flow reduces pollution and fuel use. Modern roundabouts also decrease ambient noise levels and provide an ideal location for aesthetic landscaping.
Be Frugal
With no signal equipment to install and repair, building a modern roundabout lowers materials, electricity and maintenance costs. According to the FHWA, the service life of a modern roundabout is 25 years, far greater than the 10-year service life of signal equipment.
Be Slow
When it comes to congested intersections, slower is better. By design, a modern roundabout delivers slower vehicle speeds – under 30 miles per hour. Drivers have more time to judge and react to their surroundings. Slower vehicle speeds lessen the severity of crashes and keep pedestrians safer. Although vehicles move at a slower speed, delays to motorists are actually reduced because fewer vehicles have to stop than at signalized intersections.
B&N has studied, designed and helped municipalities integrate modern roundabouts into the landscape since 2003. B&N also has experience designing and implementing more complex multi-lane modern roundabouts.
The first B&N-designed and award-winning modern roundabout opened at the intersection of Muirfield Drive and Brand Road in the City of Dublin, Ohio, in 2004. The following year, the project was named the Ohio Chapter of the American Public Works Association’s Project of the Year and was selected by the American Council of Engineering Companies for an Outstanding Achievement Award.
B&N Modern Roundabouts
Open to traffic:
Muirfield/Brand Modern Roundabout – City of Dublin, Ohio – Opened in 2004
Current modern roundabout projects in the design phase:
- State Route 161/Post Road/US Route 33
Includes two, three-lane roundabouts at freeway interchange ramps in the City of Dublin, Ohio
- Hilliard Triangle
Designing two closely-spaced, multilane modern roundabouts in a densely developed area in the City of Hilliard, Ohio
- Sawmill Parkway Extension
Designing six modern roundabouts on a four-lane suburban parkway in Delaware County, Ohio
- Avery-Muirfield Drive/Post Road Intersection
Designing a two-lane modern roundabout at a congested intersection in the City of Dublin, Ohio
- North Bend Road
Designing two modern roundabouts in Boone County, Kentucky
To learn more about B&N’s comprehensive traffic planning services, contact Steve Thieken PE, PTOE (sthieken@burnip.com) or Jim Dippel, PE (jdippel@burnip.com).
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