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Roundabouts: Safety

Many studies have found that one of the benefits of roundabout installation is the improvement in overall safety performance.  Several studies in the U.S., Europe, and Australia have found that roundabouts perform better in terms of safety than other intersection forms.  In particular, single–lane roundabouts have been found to perform better than two–way stop–controlled intersections in the U.S.   Although the frequency of reported crashes is not always lower at roundabouts, reduced injury rates are typical.  Safety is typically better at small and medium capacity roundabouts than at large or multilane roundabouts.  While overall crash frequencies have been reduced, the crash reductions are most pronounced for motor vehicles, less pronounced for pedestrians, and mixed for cyclists depending on the study and cycling design treatments.

Why do roundabouts have such a good safety record?

  1. Conflicts are reduced.  Roundabouts have fewer conflict points in comparison to conventional intersections.  The potential for hazardous conflicts, such as right angle and left turn head–on crashes is eliminated with roundabout use.   Single–lane approach roundabouts produce greater safety benefits than multi–lane approaches because of fewer potential conflicts between road users, and because pedestrian crossing distances are short.
  2. Speeds are reduced and are more consistent.  Low absolute speeds associated with roundabouts allow drivers more time to react to potential conflicts, also helping to improve the safety performance of roundabouts.  Since most road users travel at similar speeds through roundabouts, i.e., have low relative speeds, crash severity can be reduced compared to some traditionally controlled intersections.
  3. Pedestrians cross one direction of traffic at a time.  Pedestrians need only cross one direction of traffic at a time at each approach as they traverse roundabouts, 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 (and thus pedestrians have fewer places to check for conflicting vehicles).  In addition, the speeds of motorists entering and exiting a roundabout are reduced with good design.  As with other crossings requiring acceptance of gaps, roundabouts still present visually impaired pedestrians with unique challenges.

That said, roundabouts are not always safer than other alternatives:

  1. For multilane roundabouts, cycling safety at roundabouts has been found in some international studies to be poorer than at other intersections unless separate cycling or multi–use paths are provided around the outside of the roundabout.
  2. Pedestrians, especially visually impaired or blind pedestrians, can have difficulty when trying to judge gaps in traffic across entries or exits with more than one lane.

Excerpted from:  Federal Highway Administration, Roundabouts: An Informational Guide, Report No. FHWA %u2013RD%u201300%u2013067, June 2000.


Questions about roundabouts?
Contact Traffic Engineering at 480-312-7696
or email roundabouts@scottsdaleaz.gov