This research used microscopic simulation to evaluate operational performance and feasibility of signal priority for connected vehicles (CV) at a signalized intersection. CVs with signal priority were simulated with penetration levels ranging from 10% to 100% as well as with various combinations of directions being allowed to request priority. These scenarios were compared to optimized signal timings without any priority to determine the effectiveness of the system in terms of average delay. It was discovered that CV with signal priority experienced less delay than non-CV for all priority direction scenarios studied up to a certain penetration level. When all directions and major street movements in both directions are allowed to request priority, the advantage for CVs was statistically significant up to 20% CV penetration. When priority was only allowed to be requested in the direction of highest flow, CVs experienced lower delay at a statistically significant level up to 40% CV penetration levels.

A benefit-cost analysis was performed for the scenario where CV traveling in the direction of highest flow considering that CV owners may pay for priority to reduce delay to determine the viability of this type of system. The benefit-cost analysis considered the revenue generated from CVs requesting priority at intersections and the system deployment cost, and resulted in a benefit-cost ratio greater than 1 at as low as 20% CV penetration levels. Benefit-cost ratios as high as 3 were observed at 10% CV penetration level when the benefit of decreased network delay for all vehicles was included.

Arterial signal coordination performance is a major factor affecting regional travel times. Engineers manipulate offset of the coordination signal system to improve the system performance, but they need quantitative measures that can be applied to field data to better evaluate the current coordination system performance. This paper presents a visualization tool based on the Purdue Coordination Diagram (PCD)—Colored PCD—for visual assessment. A quantitative metric, VT number, is also introduced to evaluate and quantify the potential of improvement. The Colored PCD used an HSV color model to describe vehicle arrival and speed patterns. VT number is obtained using a Support Vector Machine (SVM) trained by the data from multiple simulation experiments. The results show that: 1) the Colored PCD can reveal more information than the traditional PCD; 2) VT number can indicate the potential of improvement for the subject coordination system; and 3) the proposed VT number prediction approach can give a robust VT number.

Conventional two-way signal progression models, geared to best facilitate the through traffic, often fall short of efficiency for arterials experiencing heavy turning flows at the major intersections which frequently spill over their designated turning bays and consequently block the through traffic lanes. In response to this issue, this study proposes a signal progression model, named DUALBAND, to concurrently provide green bands to both through and heavy turning flows at the target arterial. With an objective of maximizing the total green bandwidth, the proposed model can concurrently optimize phase plan, phase sequence, and offset at each intersection. Furthermore, to prevent the potential blockage to through traffic caused by the queue spillover, the DUALBAND model is capable of constraining the queue length on short left-turn bays so as to best facilitate the through movement. Using the geometry data from a field site and with extensive simulation experiments, the results reveal that the proposed model yields concurrent progression bands for both through and left-turn volumes, and also can, as expected, clearly outperform the existing MAXBAND model in reducing travel delay of those heavy turning flows.

The transition phase is generally defined as the process of switching from one timing plan to another; this process may include changes in offset, phase split or cycle length until coordination for a new timing plan is reached once again. The purpose of this paper is to develop a non-linear mathematical model to improve the performance of the transition between signal timing plans at coordinated intersections. The mathematical model proposed comprises the minimization of a social cost function, which includes a reduction in delay, gas emissions and fuel consumption by considering multiple objectives that embrace more measures of effectiveness. An ant colony algorithm is used to find the optimal parameters of coordination and to determine the time required during transition. Finally, an evaluation of the effectiveness of the new model is realized based on its ability to minimize travel time, stops, delays, and air pollution emissions and fuel consumption. Numerical results show that model proposed is effective method for to reduce social cost associated with transition period.

In designing the coordinated signal system, intersection grouping is one of critical tasks to efficiently operate signal intersections. The group size affects the bandwidth and speed of signal progression as well as vehicle platoon features. Despite the impact of the intersection grouping on the performance of signal coordination, breaking points of the corridor are predetermined or simply set less than a mile apart on major intersection in practice. In addition, the previously developed method, Coupling Index (CI), has the ambiguous criteria to determine the breaking point, requiring traffic operators to use their own judgement throughout the decision-making process. Thus, this study proposes a simple but robust decomposition method to determine intersection groups for signal coordination. To decompose the corridor, this study employs the following hierarchical clustering methods: Single Linkage Clustering, Complete Linkage Clustering and Ward’s Minimum-Variance Method. For the evaluation of the proposed methods, this study has conducted a case study along the MD-355 corridor in Maryland. The empirical results show that Complete Linkage Clustering provides the most desirable decomposition output for the target site and it outperforms the existing method, Coupling Index, with respect to increasing progression bandwidth by 6 percent and reducing delay by 9.58 percent, and the number of stops by 8.77 percent.

Signal coordination is generally recognized by traffic engineers as a beneficial strategy for improving arterial traffic progression and safety. Previous research on the criteria for establishing signal coordination plans has been focused on more objective factors such as intersection distance, arterial traffic volume, travel time, platoon dispersion and combinations of these factors. They provided useful guidance for signal coordination decisions, especially during peak hours. However, as traffic is usually less heavy during off-peak hours, the number of stops would have more influence on driver perception of traffic efficiency. This paper developed a mathematical relationship between arterial green time ratio and side-street traffic volume, which can serve as the theoretical foundation for determining signal coordination based on number of stops. The paper investigated how side-street traffic volume would affect major-street green time ratio when an isolated intersection is running semi-actuated signal operation. A probabilistic model was proposed to address this issue. The model was validated against simulation results and the upper limit of side-street traffic volume was defined for the model application. Following the proposed model, the paper briefly introduced how a traffic engineer can use the model results to make signal coordination decision based on the expected number of stops. A real case study was conducted. It was found that the model can successfully analyze the impact of side-street traffic volume on major-street green time at isolated intersections where left turns are permitted. The method for signal coordination decision can be adopted to determine the time periods of running signal coordination plans. The method and the results may be useful to traffic engineers for the effective management of traffic signal networks.

Signalized intersections are usually controlled with an aim to minimize delays, queues and lost time. The objective of signalized intersections may also be related to traffic safety or priority distribution. Relative saturation and lost time are often key parameters when calculating phase times and cycle lengths. However, when queue spillbacks block the intersection exits, the traditional Signal Phasing and Timing (SPAT) methods may not be the appropriate approach. The first aim of this paper is to investigate the effectiveness of traditional signal timing when it comes to priority distribution during various conditions. This is documented through a literature review, field observations and hypothesis testing. The second aim is to contribute towards improved distribution of priority during the most demanding conditions, mainly in severely oversaturated intersections with blockages due to queue spillbacks from downstream bottlenecks. Based on existing knowledge combined with new ideas, the last parts of this paper outlines an alternative approach, Signal Phasing and Counting (SPAC). Although the main focus is on improving priority distribution, the results from microsimulation and analytical models also suggest that delays for movements without downstream flow restrictions may be significantly reduced. 

The appropriate arterial offsets are critical for establishing quality of vehicle progression in a corridor with multiple signalized intersections. At the corridor level, vehicles departing from a queue at a traffic signal typically travel in a platoon that disperses as vehicles travel further downstream. To assess the coordination effects on an arterial road, mobility-offset relationships are developed through simulating cyclic flow profile by considering the platoon dispersion for each link in this study. To consider multi-criteria (e.g., delay and emissions) together in a single objective function, the mobility-environment relationships are identified through entire intersection spacing (i.e., links between two adjacent intersections) in the coordinated direction. Based on the mobility-offset relation as well as the mobility-environment relation, the optimization problem is formulized with intersection offsets as decision variables. To solve the problem, a dynamic programming procedure is adopted to minimize the total link costs of delay, fuel consumption and emissions. Our case study shows that the improvements in marginal cost of emissions and total objective function are obvious, which indicates the effectiveness of using total link cost as an objective for offset optimization at the corridor level. The outcomes of this integrated multi-criteria signal timing optimization can be easily implemented by traffic operators for traffic signal retiming.

Congestion of road networks is a persistent problem in almost all large and growing metropolitan areas. In the City of Toronto, a combination of transportation policies and strategies are applied to address congestion issues. One way of mitigating the impacts of congestion is through consistent, safe, and efficient control of traffic signals. Historically, the City’s traffic signal operations were guided by Standard Operating Practices (SOPs) that were inconsistent, incomplete, or out-of-date. A consolidated document to provide guidance to City staff and consultants was not available. To address this gap, a three-member Working Group was established to develop the City's "Traffic Signal Operations Policies and Strategies" document. The policies and strategies in this document complement and support the broader vision, goals and objectives of the Toronto Official Plan and Transportation Services Division Strategic Agenda, providing guidelines for the City's signal operations while promoting the consistent, safe, and efficient control of traffic signals for all road users. This paper discusses the policy developmental framework and the policy-making process used to develop the policies and strategies of traffic signal operations in Toronto. It also addresses the challenges and sensitive issues that arose during the process.

OD-BAND is a progression optimization model that can provide dedicated progression bands to major Origin and Destination (OD) flows in an arterial network. The model is an extension of the well-known MAXBAND model and is solved by a mixed-integer optimization program.  In this paper, the basic OD-BAND model is extended in a number of important ways: (a) the mathematical formulation is generalized to model all possible OD flows in an arterial; (b) phase sequence optimization is included for all intersections along the arterial; and (c) the bandwidths are weighted by the number of street segments they traverse. It is shown that this formulation can provide suitable progression bands for all major OD flows, comprising both through-bands and cross-bands. Simulation results demonstrate that OD-BAND compares favorably with existing arterial optimization models and can be used as another tool in the arsenal of signal control software.  In particular, this approach is most suitable for integrated traffic signal coordination and traffic assignment in a connected vehicles environment.

Deployments of diverging diamond interchange (DDI) have increased in recent years. Most research has focused much effort on optimizing signal timing within the DDI, but there remains a need to optimize a DDI within an existing system to ensure smooth corridor operation. This paper presents a methodology for optimizing offsets on a corridor including a single-controller DDI. This methodology uses high-resolution controller data and an enhancement to the link-pivot algorithm that deconstructs the single-controller parameters into equivalent offset adjustments. The methodology is demonstrated by its application to a 5-intersection arterial route including a DDI, and the outcomes are assessed by measurement of travel times by Bluetooth vehicle re-identification. A user benefit methodology is applied to the travel time data that considers the reliability of the travel times in addition to the central tendency. Further, the methodology is applied to O-D paths that travel to and from the freeway in addition to routes along the arterial. A total annualized user benefit of approximately $564,000 was achieved. The paper concludes by discussing how the method can also be applied to other nontraditional control schemes connected to arterials, such as continuous-flow intersections and TTI four-phase diamonds.

Diverging Diamond Interchanges (DDIs) are an innovative interchange design that are being used with increasing frequency in the United States because of the ability to frequently use existing right-of-way and infrastructure. This paper documents the state of the practice in DDI signal phasing using principles laid out in the Signal Timing Manual.  Although some literature exist on several methods of signal phasing for DDIs, inconsistency in the way they are reported leaves practitioners scratching their heads when attempting to decipher what phasing scheme to use.  In response, three fundamental phasing schemes are presented, one each for two, three, and four-critical movement volume patterns.  Each scheme is described using a consistent naming convention and, where possible, each is manipulated to provide varying coordination strategies.  In addition, concepts such as use of actuation and barriers to improve coordination are described, and methods for reducing lost time are introduced.  Other supplemental information related to preemption and pedestrians are discussed briefly.  Last, practitioners are given some basic guidance on when one phasing scheme may be more appropriate than another. 

Diverging diamond interchanges are relatively new in the United States, and signal coordination between the crossovers and adjacent intersections is challenging. This paper provides a method for remotely fine tuning offsets for a DDI and its adjacent intersections. The proposed method uses Dynamic Bandwidth Analysis Tool (DBAT) which uses actuated phase times from the signal controller and optimizes the dynamic bandwidth based on that entry data set. The authors used four performance measures to evaluate the proposed method: delay, stop severity index, maximum queue, and high resolution vehicle trajectory plots. The test results confirmed DBAT provides a better offset solution compared to other bandwidth optimization tools which generally optimize for programmed bandwidth only and do not account for early return to green due to skipped or gapped-out movements. Under the DBAT offsets, delay for the through movements on the corridor decreased by 52.8% in the northbound and 46.83% in the southbound. The average delay reduction over all measured paths for uncongested and congested scenarios was 13.88% and 3.50%, respectively.

In addition, the proposed flow and method can significantly reduce the offset retiming work process which traditionally requires visiting the study site to observe early return to green and green extension. Normally, this manual process takes more than a day, but the proposed method can be completed in less than an hour without visiting the study site. Furthermore, the proposed method can coordinate any set of movements as well as multiple travel paths. The authors believe that the proposed method and work flow will significantly help both retiming and new timing of arterial signal coordination along DDI corridors and other signal systems.