Evaluating the Operational Footprint of Alternative Diamond Interchanges

Queue spillback onto the freeway mainlines and the interactions with the adjacent intersections can have adverse impacts on traffic operation and safety, whereby the freeway becomes an expensive substitute for storing vehicles when spillback is prevalent. Thus, queue spillback onto the freeway mainlines and adjacent intersections should be analyzed as an integral part of the preliminary design selection of the service interchange. Past studies produced valuable ideas for preventing queues from reaching freeway segments, and to a smaller extent, reaching the neighboring intersections on the crossing roads. The majority of the past research focused on nonstructural remedies that are useful for improving traffic operations on existing roads, but only a few of them provided results useful in the planning and design stages. The objective of the study was to investigate the operational footprints of alternative diamond interchanges by estimating the longest queues on off-ramps and crossing roads under various geometric and traffic conditions. Ten thousand simulations of six alternative diamond designs were conducted under various geometric and traffic conditions, providing results that can assist practitioners in informed decision making. The methodology can be implemented to other interchange and intersection forms to define the operational footprint and identify potential problems in the early stages of planning and design.