Operational Study of Signalized Diamond Interchanges

This paper was developed from a research project on diamond interchanges conducted by the Texas Transportation Institute in cooperation with the Texas Highway Department. The project had the general objective of developing criteria useful m the capacity evaluation, design, and signalization of diamond interchanges. An earlier report, presented at the 40th Annual Meeting, included a procedure for evaluating the capacity of signalized diamond interchanges. This paper presents data from operational studies designed to develop criteria for the design and signalization of diamond interchanges. Four separate field studies were conducted at a signalized diamond interchange on Interstate 35W in Fort Worth, Tex. By modifications to the control equipment at this interchange, three separate signal phasing arrangements were evaluated. Also, operations with both fixed-time and traffic-actuated control equipment were studied. Recommendations are made regarding both the signal phasing and the equipment for use at signalized diamond mterchanges. The operational studies also permitted the evaluation of interchange design elements that affected traffic operations at the facility. Various aspects of design that affect operation are discussed and illustrated by a recommended design. Finally, examples illustrating the capacity-analysis, design, and signalization of diamond interchanges are presented. These examples demonstrate the apphcation of the research findings to specific design and operation problems.