Design and evaluation of actuated four-phase signal control at diamond interchanges

The operation of actuated four-phase control at diamond interchanges was investigated for moderate to heavy traffic volumes and for a wide range of ramp spacing through a CORSIM simulation combined with hardware-in-the-loop simulation technology. Three measures of effectiveness were selected for performance comparison with three-phase control: cycle length, average delay, and total stops. A new detection layout and phasing design for four-phase control were also developed. In addition, the theoretical relationship between the overlap phase duration and U-turn volume was formulated and validated. Results showed that four-phase control produced longer cycle length and higher delay than three-phase control for most traffic conditions simulated. However, four-phase control produced fewer stops than three-phase control. The mathematical formulation result showed that the operational efficiency of actuated four-phase control could be reduced as the percentage of U-turn volume increased. This characteristic was validated for all traffic volume scenarios through a simulation study, and the average delay reduction was about 5.3%. It was also shown that the performance of actuated four-phase control could be significantly improved by applying the new detection layout and phasing design introduced.