Sequence Optimization at Signalized Diamond Interchanges Using High-Resolution Event-Based Data

Signalized diamond interchanges are pairs of ramp intersections characterized by interlocked left turns and relatively close spacing. This paper describes a series of performance measures derived from high-resolution signal controller event data that can be used to optimize the internal phase sequence and offset to improve traffic flows within diamond interchanges and to qualitatively and quantitatively assess the progression of the interior movements. The new heuristic developed in this paper improves on traditional green band optimization techniques by incorporating actual demand profiles measured in the field. A field analysis was performed on a diamond interchange at I-69 and 96 th Street in northwest Indianapolis, IN, where the existing sequence data was collected and used to model the alternative sequences to identify the optimal sequence. Interior operations were improved under the optimized settings: the percent of vehicle arrivals on green increased by 19% during the 0900-1500 midday plan. Video observations were used to corroborate the data and are included in a video synthesis of the time-space trajectories. INTRODUCTION Signalized diamond interchanges are pairs of ramp intersections characterized by interlocked left turns and relatively close spacing. The interlocked left turns at a diamond interchange can experience problems when interior queues back up through the interchange and block other movements. If this occurs, the entire interchange can become gridlocked. Diamond interchanges are characterized by four external entry points (origins) and four external exit points (destinations) (1) (2). To effectively operate a diamond interchange, it is critical to examine the external origin-destination paths and evaluate their impact on the interior storage and progression. Indiana has 161 signalized interchanges across the state which equates to over 8,000 signalized interchanges nationally. There are four primary parameters in diamond interchange signal timing: