Five thousand headway measurements were taken at seven interchanges in the metropolitan Phoenix area. Saturation flow rates and lost times are given for each turning movement under different phasing conditions. A comparison is performed between saturation flow rates of conventional diamond interchanges with high design and with low design. There is a significant difference in saturation flow rates for left-turn movements from the arterial street, which indicates that high-design interchanges have higher saturation flow rates. Conventional diamond interchanges are compared with single-point diamond interchanges with respect to saturation flow rates and lost times. Single-point diamond interchanges have significantly higher saturation flow rates for the exclusive left turn from the ramp, but not for the left turn from the arterial or the arterial through movement. There is no significant difference in start-up lost times between the two interchange forms. Single-point diamond interchanges have significantly higher clearance lost times for the ramp left turn and the arterial through movement.
Abstract