The single-point diamond interchange (SPDI) has received a great deal of attention in recent years. Various analyses have been performed to evaluate the operation of the SPDI, but little field data have been collected to substantiate the input parameters used in these analyses. Research was performed to determine the saturation flow rate for the through and left-turn movements at the SPDI, and to determine the lost time per phase for the SPDI. Data were collected on 10 approaches at three interchanges in the phoenix metropolitan area. More than 3,500 headways were measured. Mean saturation flow rates of approximately 2,000 passenger cars per hour green per lane were observed for both the through and the left-turn movements at the three SPDIs studied. Mean start-up lost times between 1.5 and 2 sec per phase were measured. Clearance lost time tended to be approximately 2.5 to 3 sec per phase less than the length of the clearance interval. Total lost time varied from 20 to 24 sec per cycle. The data indicate that the large turning radii found at the SPDI tend to cause the left-turn movement to operate much like a through movement in terms of capacity. The study also indicates that long clearance intervals translate directly into increased lost time per cycle.
Abstract