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Rotary intersection: advantages and disadvantages

Short answer

A rotary is an at-grade intersection where all vehicles circulate one-way around a central island, converting crossing conflicts into merging, weaving, and diverging. Advantages: continuous flow, fewer and less severe crashes, low speed, low maintenance, and suitability for multiple arms. Disadvantages: large land requirement, unsuitable for very high volumes or heavy pedestrian flow, added travel distance, and difficulty giving priority to emergency vehicles.

Define rotary intersection. What are the advantages and disadvantages of rotary intersection?

Rotary intersection

A rotary (roundabout) is a special type of at-grade intersection in which all vehicles move in one direction around a central island (clockwise in Nepal and India, where traffic keeps left). The crossing conflicts are converted into merging, weaving and diverging movements between the approaches. Rotaries are designed to IRC:65-1976.

          |  |
        __|  |__
      /          \
 ----  ( central  ) ----
      \ ( island ) /
        --|  |--
          |  |
   one-way circulation (clockwise)

Advantages and disadvantages

Advantages

  • Removes the need for signals; traffic flows continuously, so delay is small at moderate volumes.
  • Converts all conflicts to merging, weaving and diverging, which are less severe, so crashes are fewer and less serious.
  • Low speed (about 25-40 km/h) gives safe operation and fewer injuries.
  • Suitable for junctions of 4 or more arms, and for roads carrying similar volumes.
  • Low operating and maintenance cost; no power needed and no signal failure.
  • Can handle traffic with large turning volumes.

Disadvantages / limitations

  • Needs a large area of land; not suitable where land is costly or limited.
  • Not suitable for very high volumes (more than about 3,000 PCU/h entering) or when pedestrian volume is high.
  • Pedestrian crossing is unsafe and difficult; the large diameter forces longer paths.
  • The detour adds travel distance for through and right-turning vehicles.
  • Not suitable for heavy slow traffic or where one road is much more important than the others.
  • Difficult to give priority to emergency vehicles; vehicles on straight approaches must slow down.
  • Performance drops when the approach flows are unbalanced.

✓ Answer checked by Claude Opus 5.5 (high effort)

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