Roundabouts vs intersections: why roundabouts are better

Because of the danger of intersections, the FHWA has started recommending that agencies consider implementing roundabouts instead of standard intersections during new construction or reconstruction projects. Roundabouts have proven to be a much safer, more efficient way to manage speeds while moving traffic through an intersection.

This is because roundabouts reduce the number of conflict points at an intersection from 32 to eight — a 75% reduction. Additionally, the conflict points occur while all traffic is traveling in the same direction. This substantially reduces the severity of accidents by eliminating the likelihood of sideswipe or head-on collisions. Studies have shown that converting a standard two-way stop-controlled intersection into a roundabout can reduce severe crashes by 82%, while converting a signalized intersection into a roundabout can reduce severe crashes by 78%.³

For your roundabout to effectively improve traffic flow, manage traffic speeds and reduce accidents, it’s important to install signs and pavement markings that deliver clear and consistent communication.

One of the main challenges of planning effective roundabouts is the wide entrance angle of a standard roundabout, which makes it more difficult to accurately and consistently predict the location of a vehicle relative to the traffic sign. This, in turn, makes it challenging to ensure that light will be reflected from the sign to the driver. Without reflected light, the driver may not be able to see the road sign at night, dawn and dusk.

To counteract this challenge, it’s important to use sign sheeting that creates a large, bright cone of reflectivity. This helps to ensure that light is reflected back to the driver so the sign can be seen despite a possibly disadvantaged sign location.

Here are some other things to keep in mind when you’re choosing signs and pavement markings for roundabouts:
 

• Visibility: traffic signs and pavement markings warn drivers of approaching roundabouts and can help guide them through these intersections. Effective signs and road markings share three key characteristics: brightness, conspicuity and high visibility. Studies show that fluorescent materials contribute to all three of these characteristics, are easier to see at day, night, dawn and dusk, and can help drivers recognize road signs and markings from farther away. 3M™ Diamond Grade™ DG³ Reflective Sheeting uses full-cube, fluorescent technology to deliver almost double the brightness of lower grade sign sheeting.
   
• Retroreflectivity: retroreflective pavement markings and road signs are designed to return light from a vehicle’s headlights back to the driver, making the markings and signs visible at night. This is critical for helping drivers navigate roundabouts at night, dawn and dusk.
   
• Wet retroreflectivity: wet and rainy conditions can make it difficult to see traditional pavement markings. When it’s raining, the retroreflective optics of road markings become surrounded by water instead of air. Water has a higher refractive index (RI) than air, and as a result the light from a vehicle’s headlight is spread out in a much broader, weaker cone, and very little light is reflected back toward the vehicle. This substantially reduces the visibility of the pavement marking with traditional retroreflective materials. Wet retroreflective materials, however, contain optics with a higher refractive index than traditional retroreflective materials to counteract the effects of water. Using wet retroreflective materials will increase the visibility of pavement markings in wet and rainy conditions.
   
• Durability and consistency: pavement markings undergo a great deal of adverse conditions and wear and tear. To help ensure that drivers can continue to see the markings over time, it’s critical that the pavement markings maintain their luminance, contrast and retroreflectivity.