K-113/K-18 Diverging Diamond Interchange

Kansas Department of Transportation | Manhattan, KS

In an effort to reduce congestion at the interchange of K-18 and K-113 during peak traffic conditions, the City of Manhattan and the Kansas Department of Transportation (KDOT) contracted with Benesch to perform a study with the goal of determining how to best increase capacity and improve traffic operations. Of particular concern was the significant bottleneck for southbound vehicles making left turn movements from K-113 onto the on-ramp for eastbound K-18.

Benesch gathered citizen input, performed design analysis and completed a comprehensive traffic study. This data was utilized in a value planning workshop held with City and KDOT staff. Alternatives considered during the workshop were a loop ramp, roundabouts, diverging diamond and dual left-turn lanes. Each alternative was evaluated for performance, public acceptance and cost. Benesch’s study ultimately recommended a diverging diamond interchange (DDI), including traffic signals, street lighting and ITS elements. This recommendation provided the best solution for existing and future conditions.

Following the study, Benesch provided design plans to reconfigure the existing diamond interchange to a DDI. The project included signals, lighting and signing. Pedestrian facilities were also provided.

Additional traffic analysis was completed for the DDI, using VISSIM to analyze geometrics. That data was used to confirm the number of lanes required to handle the 20-year traffic volumes. Benesch then developed construction plans for the DDI, which were used to construct the project, and also provided construction observation and inspection services for the project.

Practice Areas


  • 2019, Engineering Excellence State Winner, American Council of Engineering Companies - Kansas