TRAFFIC OPERATIONS OF BASIC TRAFFIC-ACTUATED CONTROL SYSTEMS AT DIAMOND INTERCHANGES

Abstract

This paper contains the results of field studies conducted to evaluate four types of basic, full-traffic-actuated signal control systems operated at three diamond interchanges. Two signal phasing strategies were tested: (a) three-phase and (b) four-phase with two overlaps. Two small-loop (point) detection patterns--single- and multipoint--were evaluated for each type of phasing. An assessment of these systems was conducted based on the results of statistical and observational evidence regarding their operational effects on queues and cycle lengths. Multiple and geometric linear regression were used to formulate models that relate queuing delay to traffic characteristics. Single-point detection was found to be the more cost-effective three-phase design. Multipoint detection was found to be the more delay-effective four-phase configuration. Four-phase control characteristically operates at a longer cycle length than does three-phase for a given traffic volume, and this feature may produce higher average delays unless the cycle increase is controlled to the extent that the internal progression features of four-phase can overcome this deficiency.