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City of Belleville
101 S. Illinois St.
Belleville, IL 62220
Ph: 618-233-6810

Roundabout Information
Roundabout Vs. Traffic Circles
A roundabout is a circular intersection similar to the traffic circle previously used in this country. The major differences between a traffic circle and a roundabout are:
  • Deflection: The entry and center island of a roundabout deflects entering traffic to slow traffic and reinforce the yielding process.
  • Flare: The entry to a roundabout often flares out from one or two lanes to two or three lanes at the yield line to provide increased capacity.
  • Yield at entry: At roundabouts the entering traffic yields the right of way to the circulating traffic. This yield-at-entry rule prevents traffic from locking-up and allows free flow movement.

Types of Roundabouts
There are two basic types of roundabouts:
  • Conventional roundabout: A one-way circular roadway around a curbed central island for circulating traffic, usually with flared approaches to allow multiple vehicle entry.
  • Mini-roundabout: A one-way circular roadway around a flush or slightly raised central island of up to 13 feet in diameter, usually without flared entries.

Why Use a Roundabout?
  • Aesthetics: A reduction in delay corresponds to a decrease in fuel consumption and air pollution. In addition, the central island provides an opportunity to provide landscaping.
  • Capacity: Intersections with a high volume of left turns are better handled by a roundabout than a multi-phased traffic signal.
  • Low maintenance: Eliminates maintenance costs associated with traffic signals. In addition, electricity costs are reduced.
  • Pedestrian safety: All research suggests that modern roundabouts are safer than signalized intersections for pedestrians. This safety advantage has been attributed to the slower traffic speed at roundabouts and the division of the pedestrian crossing into two stages, from the near-side wheelchair ramp out to the splitter island, and then from the splitter island to the far-side wheelchair ramp. In each stage the pedestrian has to look in only one direction to cross a one-way traffic stream. Pedestrian refuges are provided in the areas within the splitter islands.
  • Reduced delay: By yielding at the entry rather than stopping and waiting for a green light, delay is significantly reduced.
  • Safety: Roundabouts have been shown to reduce fatal and injury accidents as much as 76% in the U.S.A., 75% in Australia, and 86% in Great Britain. The reduction in accidents is attributed to slower speeds and reduced number of conflict points.