Reconciled Platoon Accommodations at Traffic Signals

The use of microprocessor-based traffic signal controllers introduced in the 1960s has allowed for the development of many new strategies to make traffic signal systems more responsive to traffic conditions. Many efforts have focused on the development of real-time, adaptive control strategies. While some of these strategies have been shown to improve intersection performance, there are several factors that have limited their deployment. Some of these include substantial capital cost, complicated calibration procedures, and the reluctance of practicing engineers to deploy strategies radically different from those currently in use. Therefore, lower cost strategies that are compatible with existing infrastructure continue to be explored. This research effort is considered to be in this category. Isolated signalized intersections, which are operated by actuated type controllers, often do not allocate green time in an optimal manner when compared to the temporal distribution of arriving traffic. Current detection schemes are typically used to provide localized detection near the intersection. At isolated intersections, which do not have coordinated timing plans for allowing progression of platoons, timing decisions are based on the binary status of localized detectors. Therefore, when platoons are forced to stop to allow the passage of a few vehicles from a minor phase, excessive stops and delays are created at the intersection. The proposed strategy uses a detection device located several thousand feet upstream from the intersection from which information is processed to identify platoons. When these platoons are detected, the controller is manipulated using low-priority preemption to allow for the platoon to progress through the intersection unimpeded. This research presents a study in which the platoon accommodation strategy was shown to reduce both the percentage of stops and delays for vehicles in the platoon without significantly impacting any of the minor approaches. This system is designed to be a retrofit to existing control equipment. Since the findings were based upon the simulated traffic, an extensive evaluation was conducted comparing field-observed platooning data with data obtained from CORSIM and the Robertson platoon distribution model. To compare field data with simulation and model data, a new procedure that looked at the percentage of vehicles arriving during a specified window was developed. Those quantitative numbers were summarized in easy to visualize charts. Platoon distribution charts were developed for 1) observed field data, 2) modeled CORSIM data, and 3) theoretical models. These charts, contained in the Appendix of the report, provide a rational procedure for estimating the upper bound on the arrival type used in the Highway Capacity calculations for signalized intersection and arterials (Chapters 9 and 11). In general, the observed field platooning characteristics were similar to the simulation model, but not exact. The CORSIM simulation model tended to have more overall platoon dispersion, which would likely provide slightly conservative estimates on benefits