Planning, Design, and Potential Pitfalls of Roundabouts

Public Works Resource
July 15, 2013 — 4,410 views  
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A roundabout is an intersection in traffic that is circular and allows for passage of vehicles without the need for a traffic signal. The road at the junction is built in a circular way around a space in the center through which the road does not pass. Around this space, vehicles continuously take the leading and intersecting roads without the need for a traffic signal to direct the flow.

The traffic entering the roundabout is reduced due to the curved structure of the roundabout and vehicles can safely pass each other. There are certain rules for road safety to be followed by traffic entering a roundabout.

Planning a Roundabout

Ideally, a roundabout needs to have a curvature sufficiently large enough to slow traffic entering it. Acute curves and smaller road width will allow efficient slowing down of traffic, but at the cost of reduced traffic flow capacity. Larger vehicles will also find it difficult to negotiate narrow roads and tight curves. So, the curve and road width also need to be designed keeping in mind the amount and the kind of vehicles passing through the roundabout.

In essence, while building a roundabout safety, traffic flow rate, and easy navigability for all types of vehicles, depending on the location, traffic density, and traffic composition should be considered. Roundabouts in less populated areas need not be very concerned with pedestrian safety as those in urban areas. They also should not have curves with small radii, but should ensure that the flow of highway-speed traffic is not bottle-necked at the roundabout.

Designing a Roundabout

Before designing a roundabout, evaluate the necessity of making one in the place where you’re planning to build it. Designing and building a roundabout should be an iterative process, be it for a single lane roundabout, multi lane roundabout, rural roundabout, or a mini roundabout. It is difficult to achieve the perfect roundabout design for any location in the first go. It is good to make a design based on initial data as well as approximations, and constantly evaluate it for road capacity, safety, and other parameters to make the necessary adjustments.

Small changes in design as well as layout can make a large difference in usage and safety. Initially, determine the best size for the intended purpose of the roundabout, the best position to build the roundabout in, and the alignment of each of the legs of the roundabout. Build the design keeping in mind these approximations. Make sure the design elements do not conflict with one another and make adjustments along the way.

Disadvantages of Roundabouts

Roundabouts eliminate the need for waiting at traffic signals and they help prevent high speed accidents from occurring at intersections. But they have their own disadvantages as well. By forcibly slowing down traffic at intersections roundabouts slowdown the overall pace of traffic entering the junction. This slow pace can, during peak traffic hours, create a dense “queue” of vehicles waiting to navigate the roundabout, which can lead to slow speed accidents. This can be especially difficult for vehicles that are in a hurry, like ambulances.

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