Why Bad Roundabouts Get Constructed
By Patrick McGrady

As I see it, there are five elements that contribute to bad roundabouts getting constructed.

First, the client does not know a good design from a bad one and they do not ensure a knowledgeable designer is being hired. "After all, it's just a circle," is a prevalent mentality. The client asks "how many have you designed," without verifying the integrity of those designs. The quality of the designs is just as important or perhaps more so than the quantity of the designs.

The second element is the nature of consultants. If you ask a consultant if he can design a levitation machine, he responds, "Sure, I have three in design right now." In an attempt to get into a new area of design (roundabouts), sometimes consultants get way over their heads. Often consultants do not realize the additional learning necessary for design of roundabouts and are not willing to absorb the cost. 

The third element is the nature of roundabouts. The design elements we see in roundabouts that rob capacity and contribute to collisions typically do not manifest themselves when the roundabout is operating at a low degree of saturation. Roundabouts are very forgiving to the user at low volumes. It may be years before a roundabout approaches saturation on one or more approaches and the poor design becomes evident. 

The fourth element is a false confidence in the traffic analysis. The performance numbers the roundabout analysis software produces are theory. The designer thinks that as long as he reflects the software input data (ICD, circulating lane width, etc) in the design the roundabout will perform at the level of service (LOS) the software suggested. This is not true. The software tells the designer, "This is the very best you can achieve." The LOS and safety of a constructed roundabout depends upon the skills of the designer to produce excellent geometry, signing, striping, and landscape plans.

The fifth element is getting the roundabout designed per the contract plans. Often the field inspector is not familiar with roundabouts and makes decisions that compromise the design of the roundabout.