Delays and lane closures are expected as crews begin work Tuesday to make changes to the roundabout at Washington Avenue and Independence Drive.
City Engineer Jonathan Zimmermann expects that the roundabout will remain open during construction, other than one “outlet” lane. The lane that is closed will change depending on which island is being constructed.
Zimmermann told aldermen last week that some trucks can’t make immediate right turns do to an inaccurate design.
He said that there are no problems for most of the trucks making right turns, or for any trucks going straight or turning after entering the roundabout.
The city is not responsible for the cost to modify the intersection, Zimmermann added.
Plans call for a modification to islands that split traffic between vehicles leaving and vehicles entering the roundabout.
Those islands will be mountable, similar to the center circle, which has a sloping curb that is designed for large trucks to drive over.
According to Zimmermann, during construction vehicles can enter the roundabout from any direction, but during work there will be one exit closed.
Motorists can exit in the two open outlets, but there still may be some temporary closures or delays.
He noted it takes about four hours to change each splitter island.
The intersection at Independence Drive and Main Street was completed Aug. 23.
Zimmermann said Cochran engineers use a program to predict turning movements within an intersection, but the correct turning radius was not applied.
He added that any future roundabouts, including the intersection proposed on Prairie Dell Road at the entrance to East Central College, will be designed more conservatively.
Roundabouts in some communities require that tractor-trailer drivers wanting to make an immediate right turn must first enter the roundabout and circle through before turning, according to Zimmermann.
He noted that would alleviate any turn radius issues.
The traffic light at the intersection has alternated between both a flashing four-way lighted intersection and a timed light intersection several times during the past four years.
The light was changed to a four-way stop during only evening and night hours in April 2008, and then later to a four-way stop 24 hours a day.
Some residents have complained that the four-way stop is unsafe and confusing.
City officials have said roundabouts are safer and less costly to maintain than a lighted intersection.
At roundabouts, vehicles travel counterclockwise around a raised center island, with entering traffic yielding the right of way to circulating traffic. Once there is a gap in traffic, drivers enter the circle and proceed to their exit. If there is no traffic in the roundabout they enter without yielding.
Roundabout intersections are “pedestrian friendly,” officials have said.