Rotary Island in Road

Rotary intersections or roundabouts are special from at-grade intersections laid out for the movement of traffic in one direction around a central traffic island. Essentially all the major conflicts at an intersection namely the collision between through and right-turn movements are converted into milder conflicts namely merging and diverging. The vehicles entering the rotary are gently forced to move in a clockwise direction in an orderly fashion. They then weave out of the rotary to the desired direction.

Advantages:

The key advantages of a rotary intersection are listed below:

1. Traffic flow is regulated to only one direction of movement, thus eliminating severe conflicts between crossing movements.

2. All the vehicles entering the rotary are gently forced to reduce the speed and continue to move at a slower speed. Thus, none of the vehicles need to be stopped, unlike in a signalized intersection.

3. Because of the lower speed of negotiation and elimination of severe conflicts, accidents, and their severity are much less in rotaries.

4. Rotaries are self-governing and do not need practically any control by police or traffic signals.

5. They are ideally suited for moderate traffic, especially with irregular geometry, or intersections with more than three or four approaches.

Disadvantages:

Although rotaries offer some distinct advantages, there are few specific limitations for rotaries which are listed below:

1. All the vehicles are forced to slow down and negotiate the intersection. Therefore, the cumulative delay will be much higher than a channelized intersection.

2. Even when there is a relatively low traffic, the vehicles are forced to reduce their speed.

3. Rotaries require large areas
of relatively flat land making them costly in urban areas.

4. The vehicles do not usually stop at a rotary. They accelerate and exit the rotary at relatively high speed. Therefore, they are not suitable when there is a high pedestrian movement.