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Actuated signal operations for congested conditions were evaluated with a simulation study at diamond interchanges. Both three-phase and four-phase with two-overlap phasing strategies were employed, with four ramp spacings and traffic patterns. The performance difference was discussed with throughput, average delay, and total stops. Results showed that four-phase control gave less or comparable average delay (or more throughput) for most traffic patterns at ramp spacings of 122 m or more. Three-phase control gave less delay (or more throughput) when an interchange had a balanced traffic pattern from all external approaches. In terms of stops, four-phase operation gave less stops than three-phase operation for all congested conditions investigated. Analysis results indicated that marginal operational benefits could be obtained when ramp spacing was designed between 122 and 183 m. In addition, several regression models were developed for use in performance estimation for congested traffic conditions. The test results showed that the models could provide good performance estimation of congested signal operation at diamond interchanges. DOI: 10.1061/(ASCE)0733-947X(2006)132:10(790) CE Database subject headings: Simulation; Traffic signals; Interchanges.

Chapter 16 of the Highway Capacity Manual 2000 (HCM 2000) includes models and procedures for calculating capacity and delay at signalized intersections. However, the procedures do not provide estimation of the optimal cycle length which would result in the minimal intersection delay. A quick estimation method for determining the cycle length is described in Appendix A, Chap. 10 of the HCM 2000 for planning level applications. In this method, a simple equation is used to estimate the cycle length if it is not available. However, the estimated cycle length may not be the optimal cycle length from the point of view of achieving minimum intersection delay. To develop a new cycle length model, the Webster's minimum delay cycle length model is first considered. However, based on our study, Webster's minimum delay cycle length model overestimates the optimal cycle length compared to the results from the HCM 2000 delay calculation method, especially under high traffic volume conditions. After investigating three new models developed during this study, an exponential-type cycle length model is recommended. Based on a series of CORSIM simulation runs, the cycle length predicted by this model provides better results than the current quick estimation method of the HCM 2000. DOI: 10.1061/(ASCE)0733-947X(2005) 131:12(890) CE Database subject headings: Delay time; Intersections; Traffic signals; Traffic management.

The performance of three traffic analysis tools: CORSIM, SIMTRAFFIC, and SYNCHRO was investigated for application to diamond interchanges. Actuated signal operation was implemented for different ramp spacings and traffic patterns. The performance differences were discussed for three performance measures: Cycle length, average delay, and total stops. Our research showed that the two microscopic models (CORSIM and SIMTRAFFIC) produced similar performance, but the macroscopic program SYNCHRO provided different performance trends. It was found that SYNCHRO 4 and SIMTRAFFIC produced different phase splits for the same input data. Therefore, there is a possibility that estimated delay (or stops) performance could vary depending on the model selected. Our results also indicate that SYNCHRO 4 apparently does not reflect some progression effects properly, thus the application of SYNCHRO 4 for diamond interchanges should be used with caution. Either SIMTRAFFIC or CORSIM used in conjunction with hardware-in-the-loop simulation should be used for analysis of actuated diamond interchanges. It was also found that SIMTRAFFIC tended to model queue spillback conditions more restrictively at the upstream intersection than did CORSIM or SYNCHRO. DOI: 10.1061/(ASCE)0733-947X(2004)130:3(304) CE Database subject headings: Simulation models; Interchanges; Traffic signals.

Parallax error is a distance-related measurement error when the measurement has to rely on field of view, such as video-image systems. This paper provides a detailed investigation of the geometric elements associated with parallax error in video-image systems. A field-of-view calibration model is presented based on a study of various geometric elements, including camera height, camera location, view of image, and vehicle dimension. The study found that parallax error ranges between 10 and 50% based on normal camera setup. The model presented provides a better understanding of the parallax error; thus the accuracy of distance-related measurements could be improved when video-image systems are deployed. The proposed model has special application values at signalized intersections where video-image systems are deployed. One of the applications is to identify the range of possible blockage by a leading vehicle, which is one of the major causes of missed detections. Another application is to identify the conditions that result in vehicle occlusion, which is a source of false detections. CE Database keywords: Errors; Measurement; Imaging techniques; Transportation engineering.

Actuated signal operations for congested conditions were evaluated with a simulation study at diamond interchanges. Both three-phase and four-phase with two-overlap phasing strategies were employed, with four ramp spacings and traffic patterns. The performance difference was discussed with throughput, average delay, and total stops. Results showed that four-phase control gave less or comparable average delay (or more throughput) for most traffic patterns at ramp spacings of 122 m or more. Three-phase control gave less delay (or more throughput) when an interchange had a balanced traffic pattern from all external approaches. In terms of stops, four-phase operation gave less stops than three-phase operation for all congested conditions investigated. Analysis results indicated that marginal operational benefits could be obtained when ramp spacing was designed between 122 and 183 m. In addition, several regression models were developed for use in performance estimation for congested traffic conditions. The test results showed that the models could provide good performance estimation of congested signal operation at diamond interchanges. [ABSTRACT FROM AUTHOR]

Chapter 16 of the Highway Capacity Manual 2000 (HCM 2000) includes models and procedures for calculating capacity and delay at signalized intersections. However, the procedures do not provide estimation of the optimal cycle length which would result in the minimal intersection delay. A quick estimation method for determining the cycle length is described in Appendix A, Chap. 10 of the HCM 2000 for planning level applications. In this method, a simple equation is used to estimate the cycle length if it is not available. However, the estimated cycle length may not be the optimal cycle length from the point of view of achieving minimum intersection delay. To develop a new cycle length model, the Webster’s minimum delay cycle length model is first considered. However, based on our study, Webster’s minimum delay cycle length model overestimates the optimal cycle length compared to the results from the HCM 2000 delay calculation method, especially under high traffic volume conditions. After investigating three new models developed during this study, an exponential-type cycle length model is recommended. Based on a series of CORSIM simulation runs, the cycle length predicted by this model provides better results than the current quick estimation method of the HCM 2000. [ABSTRACT FROM AUTHOR]

The performance of three traffic analysis tools: CORSIM, SIMTRAFFIC, and SYNCHRO was investigated for application to diamond interchanges. Actuated signal operation was implemented for different ramp spacings and traffic patterns. The performance differences were discussed for three performance measures: Cycle length, average delay, and total stops. Our research showed that the two microscopic models (CORSIM and SIMTRAFFIC) produced similar performance, but the macroscopic program SYNCHRO provided different performance trends. It was found that SYNCHRO 4 and SIMTRAFFIC produced different phase splits for the same input data. Therefore, there is a possibility that estimated delay (or stops) performance could vary depending on the model selected. Our results also indicate that SYNCHRO 4 apparently does not reflect some progression effects properly, thus the application of SYNCHRO 4 for diamond interchanges should be used with caution. Either SIMTRAFFIC or CORSIM used in conjunction with hardware-in-the-loop simulation should be used for analysis of actuated diamond interchanges. It was also found that SIMTRAFFIC tended to model queue spillback conditions more restrictively at the upstream intersection than did CORSIM or SYNCHRO. [ABSTRACT FROM AUTHOR]