Comparison of Two Protected-Permitted Lead-Lag Left-Turn Phasing Arrangements

摘要

The report documents an analysis of the operations of a special type of lead-lagleft-turn phasing sequence developed and used by traffic engineers in Dallas and Richardson, Texas. The phasing, known as the Dallas phasing, is prohibited by existing standards for left-turn phasing set forth in the Manual for Uniform Traffic Control Devices (MUTCD). The objective of the research was to use field and simulation data to evaluate the operational characteristics and benefits of the type of left-turn phasing arrangement. Operational data were collected at four intersections in the Dallas area that utilized the phasing. Measured and predicted stopped delays were used as the primary operational measures of comparison. The results of the study indicate that the Dallas phasing can be accurately modelled with existing left-turn models. In addition, the study presents new values for several parameters used in protected-permitted left-turn models; i.e., values for critical gap, left-turn headway, and the average number of sneakers. The results of the study also indicate that the Dallas phasing results in less delay for both left-turning and through movements than the MUTCD phasing, and that at intersections along high volume coordinated arterial streets, the Dallas phasing offers significant operational benefits.