While roundabouts are a relatively new type of intersection in Iowa, they are becoming more common as evidence of their benefits grows. Improved traffic flow, aesthetics and cost savings make roundabouts a good idea, and the safety gains are compelling.

Standard two-lane conflict points Standard two-lane conflict points
Single-lane roundabout conflict points Single-lane roundabout conflict points

Fewer crashes and less severe crashes

Roundabouts benefit from good geometry, exhibiting only a fraction of the troublesome crash patterns typical of right-angle intersections. A typical four-legged intersection has 32 vehicle-to-vehicle conflict points and 24 vehicle-to-pedestrian conflict points. By comparison, a four-legged roundabout has only eight vehicle-to-vehicle conflict points and eight vehicle-to-pedestrian conflict points. This is an approximate 70 percent reduction in conflict points. In addition, since all vehicles are traveling in the same direction and at a lower speed in a roundabout, crashes are generally rear end or sideswipe in nature. Left-hand, right-angle (T-bone) and head-on crashes are virtually eliminated by a roundabout. The illustrations at the top of this page show the conflict points of a standard intersection and a typical roundabout. Studies by the Insurance Institute for Highway Safety show that roundabouts provide a:

  • 90 percent reduction in fatal crashes;
  • 76 percent reduction in injury crashes;
  • 30 to 40 percent reduction in pedestrian crashes; and
  • 10 percent reduction in bicycle crashes

Lower vehicle speeds

A standard stop sign or traffic signal controlled intersection always has at least one direction of traffic stopped. A roundabout uses yield-at-entry traffic control to eliminate stopping when it is not required.

Less vehicle pollution

Vehicles entering a roundabout must yield at entry, but are not required to stop if the roundabout is clear. This eliminates some stop-and-go traffic associated with stop sign or traffic signal controlled intersections. This leads to fewer vehicles idling while stopped at an intersection.

Lower maintenance costs as compared to a traffic signal

A traffic signal requires electricity 24 hours a day. In addition, the signals need maintenance by field personnel for burned out lights, loop detector replacement, etc. A typical roundabout generally only needs electricity for streetlights at night and maintenance for landscaping, if included.

Increased landscaping opportunities

A standard intersection requires a large paved area to accommodate all the turning movements. A roundabout provides opportunity to landscape the center island, providing green space within the intersection.

Pedestrians cross one direction of traffic at a time

Pedestrians need only cross one direction of traffic at a time at each roundabout approach, as compared with two-way and all-way stop-controlled intersections. The conflict locations between vehicles and pedestrians are generally not affected by the presence of a roundabout, although conflicting vehicles come from a more defined path at roundabouts. In addition, the speeds of motorists entering and exiting a roundabout are reduced with good design. As with other crossings that require acceptance of gaps in traffic flow, roundabouts still present visually-impaired pedestrians with unique challenges.


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