A Comparative Analysis of Diverging Diamond Interchange Operations

Abstract

Across the country, increasing travel demand is steadily putting additional strain on the existing roadway infrastructure. The need to provide additional capacity is constantly at odds with the potential impacts that transportation improvements have on surrounding developments. The diverging diamond interchange (DDI) concept is being considered as an alternative that may provide extra capacity while also reducing the amount of space required for implementation. This presentation will discuss the operational benefits of the DDI. The DDI appears to greatly improve operations along the crossroad and at the ramp terminals. The impact of the DDI traffic flow patterns at mainline merge points and on ramp meters will also be discussed. The operations of the DDI will be compared to the operations of other interchange types which will also allow for a planning-level assessment of the differences in the interchange footprints. This interchange concept is based on a standard diamond interchange with the key difference being a shift in the crossroad traffic in the interchange. Traffic on the crossroad crosses paths twice as traffic is shifted to the left side of oncoming traffic allowing left turn movements to occur without impeding oncoming traffic. The presentation is intended to introduce engineers to the operational benefits of the diverging diamond interchange concept and to identify when and where the greatest amount of benefits may be realized.