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Say no to roundabout

March 8, 2017
Island Reporter, Captiva Current, Sanibel-Captiva Islander

To the editor:

The regional daily ran an article recently that stated that the Sanibel intersection of Periwinkle Way and the causeway exit is number one on the list of intersections being considered by Lee County for converting to a roundabout. This must be opposed by all Sanibel residents and our Sanibel government.

The successful operation of an existing, or planned roundabout depends on a number of factors that must be accurately known to prevent congestion and accidents. A roundabout brings together conflicting traffic streams, allows the streams to safely merge and traverse the roundabout, and exit the streams to their desired directions. The geometric elements of the roundabout provide guidance to drivers approaching, entering, and traveling through a roundabout.

Drivers approaching a roundabout must slow to a speed that will allow them to safely interact with other users of the roundabout, and to negotiate the roundabout.

The width of the approach roadway, the curvature of the roadway, and the volume of traffic present on the approach govern this speed. As drivers approach the yield line, they must check for conflicting vehicles already on the circulating roadway and determine when it is safe and prudent to enter the circulating stream.

The widths of the approach roadway (single lane or dual lane) plus the number of large trucks (which move slower and swing wider) determine the number of vehicle streams that may form side by side at the yield line and govern the rate at which vehicles may enter the circulating roadway. The size of the inscribed circle affects the radius of the driver's path, which in turn determines the speed at which drivers travel on the roundabout. The width of the circulatory roadway determines the number of vehicles that may travel side by side on the roundabout. Finally the number of exit points and number of lanes at those exit points impacts rates of traffic flow.

Also affecting the number of vehicles that can be accommodated is the demographics of the vehicle drivers. Senior citizens tend to be more cautious so take more time to enter the roundabout and go around at reduced speeds.

Finally, peak use times dramatically affect the design of a roundabout that may backup due to excess traffic that reduces driver reaction time to opportunities to enter the roundabout.

Add to these factors the rate of flow on the causeway and through the toll both area at peak exit time plus the que backup on Periwinkle, you can be assured of a lower rate of vehicle flow than standard engineering analysis of roundabouts would suggests. In other words, do not believe any analysis that Lee County traffic engineers provide that suggest Sanibel should be the number one candidate for a roundabout. Our Sanibel police do a marvelous job of keeping traffic flowing under difficult seasonal conditions and I can assure you that a roundabout would be a disaster. For the record, I consider myself an exceptional experienced driver of roundabouts having lived in France for three years and vacationed by auto in England for more than 16 years.

Ron Dudley




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