US Highway 61 and Missouri Route 47 Interchange Design Study Identifies Congestion Mitigation


  • Local Governments
  • State Agencies


  • Bridges + Structures
  • Engineering
  • Roadways + Interchanges
  • Traffic + Safety
  • Transportation


  • Troy, Missouri

An initial comprehensive review of the US Highway 61 and Missouri Route 47 interchange was completed to improve the interchange operations and to identify congestion mitigation measures for Route 47 corridor progression between East Cherry Street and Main Street in Troy, Missouri. The Missouri Department of Transportation partnered with HR Green to review operating conditions and traffic volumes for both existing and future planning 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 results 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 traffic movements at the US 61 interchange, particularly the northbound to westbound movement. Traffic flow is restricted with a three-lane bridge over the highway and 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 Highway 61 and Missouri Route 47 interchange. A review of the traffic operations, property impacts, constructability, and constructions 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.

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