Roundabout
Innovative Intersections
What is a roundabout?
A modern roundabout is a circular intersection where traffic moves counterclockwise around a central island. Vehicles entering the roundabout must yield to those already circulating.
Roundabouts can be used in both urban and rural settings and come in three configurations: mini, single-lane, and multi-lane.
Mini roundabout
Single-lane roundabout
Multi-lane roundabout
Design principles
The modern roundabout is characterized by the following basic principles:
Shape
Generally circular shape with counterclockwise traffic flow
Yield-at-Entry
Vehicles approaching the roundabout must wait for a gap in the circulating flow, or yield, before entering the circle
Slow speeds
Through geometric curvature and deflection, the traffic is directed or channeled to the right with a curved entry path into the circulatory roadway.
Design characteristics
Roundabouts are a versatile choice for intersection control because the geometry can be modified to suit the constraints of each intersection. While roundabout geometry is flexible, there are certain design characteristics that all roundabouts share and some that are site dependent.
Common to all roundabouts
Central island: Directs vehicles around circulating lane
Splitter islands: Separates approach and exit lanes in advance of the intersection
Lighting, signing, & pavement markings: Improves intersection visibility and provides needed information to intersection users.
Site dependent
Truck aprons: Accommodates large vehicle trailers
Crosswalks, sidewalks, & shared use paths: Accommodates pedestrians and bicyclists
Landscaping & hardscaping: Can be used to enhance intersection visibility and beauty
What are the benefits of roundabouts?
Enhanced safety
Reduced number of conflict points.
- Roundabouts reduce fatalities by 90% by eliminating crossing conflict points and head-on crashes.
- Roundabouts significantly reduce the total number of conflict points in an intersection, which means fewer opportunities for crashes.
| Conflict points | Conventional intersection | Roundabout |
| Diverging | 8 | 4 |
| Merging | 8 | 4 |
| Crossing | 16 | 0 |
| Total | 32 | 8 |
Slower vehicle speeds
- Slower vehicle speeds give drivers more time to make decisions.
- Slower vehicle speeds improve pedestrian and cyclist outcomes when a crash does occur.
Source: USDOT
Operational performance
- Roundabouts improve traffic flow by using a yield-on-entry system.
- Drivers only need to come to a stop when there isn’t enough room for them to safely enter the intersection.
- Less stopping means fewer delays and less congestion.
- Vehicle 1: Safely enters intersection.
- Vehicle 2: Safely enters the intersection.
- Vehicle 3: Already in the intersection, approaching vehicles must yield.
- Vehicle 4: Must yield to Vehicle 3 to enter safely.
- Vehicle 5: Approaching the intersection but is still far enough away to not affect the other drivers.
Resiliency
- Roundabouts operate without power, functioning during outages and freeing emergency crews to focus on signalized intersections.
Placemaking opportunities
- Roundabouts offer spaces for landscaping, hardscaping, signage, or public art, allowing for collaboration with local agencies to enhance community character.
Environmental considerations
- Roundabouts allow continuous traffic flow, reducing the time vehicles spend idling.
- This leads to lower vehicle emissions and fuel consumption contributing to a cleaner environment.
Are roundabouts appropriate everywhere?
Roundabouts are excellent solutions for many intersection challenges, making them increasingly popular. However, they might not be the best option in every situation. Common concerns are listed below, but most can be addressed with careful design and proper outreach. Comprehensive planning and design are essential to ensure roundabouts are suitable for a specific intersection.
Learn more about roundabouts
TxDOT’s Design Division is available to support implementation with resources for peer reviews, concept sketches, ICE reviews, training, and more.
Request assistanceDesign Aids - coming soon
- Performance checks
- Signage
- Spiral design
- High-speed approaches
Public education flyers - coming soon
- General overview
- How pedestrians and bikes use roundabouts
- How emergency vehicles use roundabouts
- How freight uses roundabouts
- Frequently asked questions (FAQs)