Essay On Roundabout

Across the world, traffic growth and congestion continue to outpace growth in highway capacity. A large amount of this congestion occurs at intersections, rather than along the links between intersections. A roundabout is a type of road junction at which traffic enters the stream around a central island after first yielding to the circulating traffic.

Roundabout is an effective traffic control measure. It enhances intersection capacity and safety and has many other benefits like reducing number of conflicting points with decreased delay and greater efficiency than traffic signals. The main reason for constructing roundabouts is greater intersection safety, as various studies have shown that they can reduce road accidents by about 75% compared

Roundabout is less safe for pedestrian compare to other intersection control. To minimize ped accidents at entry and exit, entry and exit speed of vehicle should be less.

2. Traffic Operation at Roundabouts

The study of intersection operations involves examination of how well the intersection services the volume of traffic that flow through it each day. The design of the intersections should be with sufficient capacity for existing and future traffic volumes that also minimize the delay for users.

2.1. Roundabout Capacity

Capacity is most important measure to estimate performance of roundabout. Capacity of roundabout is depends on two factors:

1. The circulating flow on the roundabout that conflicts with the entry flow

2. Geometric elements of the roundabout.

The capacity of whole roundabout is not fixed. Roundabout is designed to operate at less than 85% of its capacity. Because if flow increase this value then delay and queues will be more.

2.1.1 Urban compact roundabouts

Typical inscribed circle diameter of these roundabout is 25-30m. All legs have single lane at entry.

Equation developed by Brilon et al. (1997), for capacity calculation of urban compact roundabouts is

Qe 1218 −0.74 Qc

Where: Qe = entry capacity, pce/h

Qc = circulating flow,