A traffic rotary or rotary intersection or say a roundabout is a specialized form of road intersection at grade, where all converging vehicles are forced to move around a large central island (Rotary Island) in one direction (clockwise direction) before they can weave out of traffic flow into their desired direction.
The main objects of providing a rotary are to eliminate the necessity of stopping for crossing streams of vehicles and to reduce the area of conflict.
Advantages of Traffic Rotary
The advantages of providing a traffic rotary(Roundabout) are as follows:
- Orderly and disciplined traffic flow is provided by the one-way movement.
- Frequent stopping and starting of vehicles are avoided.
- Direct conflict is eliminated.
- All turns can be made with ease.
- A rotary is especially suited for intersection legs ranging from 4 to 7.
- For moderate traffic, rotaries are self-governing and need no control by police or traffic signals.
- The capacity of rotary intersection is the highest of all other intersections at grade.
Disadvantages of Traffic Rotary
The disadvantages of providing traffic rotary(Roundabout) are as follows:
1. Rotary requires comparatively large of land. So where space is limited and costly, the total cost may be high.
2. Where the pedestrian traffic is large, the rotary by itself cannot control the traffic and needs control by traffic police. If the vehicular traffic has to stop to allow the pedestrian to cross, the main purpose of rotary has defected.
3. At the places of mixed traffic, the design of rotary becomes too elaborate and the operation and control of traffic become complex.
4. Where the angle of intersection of two roads is too acute or when there are more than seven intersecting roads, rotaries are unsuitable.
5. When the distance between the intersections on important highways is less, a rotary becomes troublesome.
6. At the places of mixed traffic, there is a tendency to violate the traffic regulation of clockwise movement.
7. Where the traffic volume is very low, construction of a rotary cannot be justified.