Route 47/61 Interchange Study

An initial comprehensive review of the US Highway 61 and Missouri Route 47 interchange was completed to identify congestion mitigation measures to improve the interchange operations, as well as the Route 47 corridor progression between East Cherry Street and Main Street in Troy, Missouri. HR Green was retained by the Missouri Department of Transportation to review existing operating conditions and characteristics of the interchange, and traffic volumes for both existing and future planning horizon conditions.

The population surge in the early 2000s resulted in increased congestion at the US 61 and Route 47 interchange. A heavy northbound to westbound movement during the afternoon peak traffic periods currently results in queues on the US 61 off-ramp which extend to the gore, resulting in slow traffic on the northbound auxiliary lane adjacent to the high-speed northbound traffic lanes on US 61. This auxiliary lane serves as a deceleration lane for off-ramp traffic at Route 47, as well as an acceleration lane for on-ramp traffic at Old Cap Au Gris, resulting in a short weaving segment between the ramps. The three-lane bridge section and close spacing of the interchange ramps and adjacent full access intersections result in poor traffic flow and congestion, particularly during the afternoon peak traffic period. The overall Route 47 corridor through the City of Troy is challenged with increased heavy westbound traffic movement from the interchange, with multiple traffic signalized intersections along the corridor.

HR Green was responsible for traffic data collection, including hourly traffic volumes, crash history, and GPS enabled travel time to understand the traffic flow deficiencies throughout the corridor. Nine preliminary concepts were vetted to determine the top four interchange options to further investigate with detailed traffic modeling tools such as VISSIM, Synchro, SIDRA, and HCS.  Each of the four design alternatives, including the “Do Nothing” option was reviewed to identify a preferred solution at the US 61 and Route 47 interchange. A review of the traffic operations, property impacts, constructability, and construction costs associated with each of the design options revealed that a Diverging Diamond Interchange (DDI) would ultimately provide the most benefits towards meeting the overall project goals.

HR Green was also responsible for conceptual design plans to provide additional construction details and estimated construction costs of the DDI and recommended improvements along Route 47 between Turnbull Lane/Merlin Drive and East Cherry Street, including typical roadway, ramp, and bridge ramp sections, plan view of the improvements, vertical profiles, traffic signal and lighting layout, advanced sign layout, and cross-sections.