RETROFITTING CLOSELY SPACED INTERSECTIONS USING THE PEANUT- TURBO ROUNDABOUT CONCEPT

St. Charles County, Missouri is located approximately 30 miles from the City of St. Louis and boasts a population of just over 350,000. Interstate 70 traverses the County and provides key access to the region. The County Highway Department desired to improve access to I-70 by extending Deer Creek Drive from Highway P to the I-70/Bryan Road Interchange. Currently, Bryan Road is a key arterial south of I-70 but terminates at the north outer road (typically referred to as West Terra Lane). West Terra Lane is located approximately 375 feet from the Westbound I70 On/Off Ramp at Bryan Road. Due to the close proximity of West Terra Lane to the interchange ramps, several traditional intersection designs were reviewed to determine if acceptable traffic operations could be achieved. Most of the design concepts, however, required extensive right-ofway beyond what the County desired. Several roundabout concepts were then reviewed, but were unable to provide acceptable traffic operations. Non-standard roundabout alternatives were then analyzed to determine if acceptable traffic operations could be achieved, while at the same time minimizing both right-of-way and access-related issues. After review of several concepts, the Peanut-Turbo Roundabout concept was found to meet all three of the County’s goals. The focus of this presentation/paper will be to highlight the roundabout options that were considered and the process used (including analysis with the software packages Synchro, SIDRA INTERSECTION, and VISSIM) to assist the design team in determining the appropriateness of the various alternatives.