Actuated Traffic Signal Performance Evaluation along Arterials using Wi-Fi Travel Time Samples and High-Resolution Traffic Signal Events Data

Understanding traffic progression on arterials is critical for traffic signal control and urban traffic management. Traffic conditions are highly dynamic and evolve over time. Therefore, it is necessary to evaluate the arterial’s performance periodically to determine how well a traffic signal system is functioning. Arterial performance is conventionally evaluated based on travel time/speed collected via the probe vehicles. New approaches based on high-resolution traffic signal events have been proposed by a group at Purdue University, based on the Purdue Coordination Diagrams (PCDs). Both traditional arterial travel times/speeds and the PCDs can effectively reflect the level of traffic progression on arterials, while some practical questions have been raised about how to synthesize these two methods. The framework proposed in this paper integrates two types of performance measures by defining new multi-intersection coordination diagrams to examine traffic signal performance. The multi-intersection coordination diagram under different speeds can provide a straightforward tool for informed offset adjustments of actuated traffic signal coordination. In contrast, the state-of-the-practice traffic coordination performance analysis relies on fixed timings and empirical fine-tuning in the field. It is expected that these efforts can provide new insights to practitioners on how to use emerging traffic data better to improve the performance of actuated traffic signal operations on arterials.

Impact of Detector Configuration on Performance Measurement and Signal Operations

In recent years, automated traffic signal performance measures (ATSPMs) have emerged as a means of developing situational awareness of traffic conditions at intersections and assessing the quality of signal operations. As a growing number of agencies are adopting the technology, there is a need to understand how detector configurations can influence the outcomes of an analysis using ATSPM. Current practices with regard to detector configuration vary considerably from one agency to another; at one extreme, agencies may use one single detector input channel per phase without considering where the detectors are located, whereas at the other extreme, some agencies may utilize all possible channels to observe each individual lane at multiple positions. There are also variations in the design of detection zones (lengths and positions). This study takes on the problem in two parts. The first of these examines the impact of stop bar detection zone length and lane- or approach-based detector assignment on the ability of performance measures to identify accurately whether split failures occur. The second part examines the impact of setback detector distance on the use of a “percentage on green” metric that serves as a proxy measurement of the number of stops. The paper presents recommendations for performance measure calibrations and detector configurations that follow from these outcomes.

Estimating Pedestrian Impact on Coordination of Urban Corridors

Pedestrian walk timings at most U.S. traffic signals are run in concurrence with relevant signal phases for vehicular traffic. This usually means that signal operations coordinated for the major street can be interrupted by a pedestrian call. Such an interruption may in practice last for a few minutes, thus causing increased delays and stops for major traffic flows. An alternative to this design is to increase the cycle length and embed pedestrian timings within the ring-barrier structure of the prevailing coordination plan. Both approaches have advantages and disadvantages. A fresh approach offered by this study is a comprehensive experimental design and holistic performance evaluation perspectives. The study examines the two abovementioned treatments of pedestrian timings for a small corridor of five intersections in Utah. The experiments have been done in a high-fidelity microsimulation environment with the Software-in-the-Loop version of the field controller (Econolite ASC/3). Findings show that either approach works well for very low traffic demands. When the traffic demand increases findings cannot be generalized as they differ for major coordinated movements versus overall network performance. While major-street traffic prefers no interruption of the coordinated operations, the overall network performance is better in the other case. This can be explained by the fact that avoiding interruptions is usually achieved at the expense of longer cycle length, which increases delay for everyone in the network.

Smart signals in heterogeneous traffic conditions

Major urban corridors in Indian cities are carrying significantly high traffic leading to near saturated conditions for extended peak hours. As mixed landuse and major trip attracting/generating establishments are generally observed to be located along such corridors for better accessibility, significant side friction is also observed along these corridors. Among various measures to improve the throughput along such corridors, signalized intersections seem to be the most preferred intervention for intersection control. Although frequent occurrence of such traffic signals and non-coordinated signal phases have in turn made the whole situation more complex. To overcome this challenge, variations of smart signals are being proposed by technology and traffic enterprises globally. Generally, smart interventions in operation of signalised intersections require communication among vehicles and control system through various sensors and applications of Intelligent transport services (ITS). Smart signal operations require the sensors grouted in pavement or attached with camera to share the relevant data in real time basis with central command and control centre. With adaptive signal operations, it is attempted to schedule signal phases in such a way that green phase of every cycle generally experiences near saturated flow conditions. The smart cities mission (SCM) of India, covering around 100 cities also focuses upon improving the urban mobility through various measures including smart signals. Some of the popular proposals relating to smart operation of signalised intersection across shortlisted smart cities include adaptive and coordinated traffic signals. It is understood that traffic signal optimization is not a one-time action but rather a continuous process, as data archiving, data crunching, research and adaptations are indispensable for its success. As the geometry, location and setting of each intersection in every network is bound to be unique, the optimization process needs to consider the same. The literature and case study of Indian city Bhubaneswar (ranked first in nationwide smart city challenge) revealed that challenges specific to Indian driving conditions are major cause of worry for yielding stated benefits of smart signals. Factors like varying hierarchy and functions along major arterial corridors, fluctuating carriageway width and quality, considerable side friction within right of way, heterogeneity in vehicular mix, significant variation in peak hour directional flows leading to tidal flow, surrounding network characteristics and efficacy of optimisation techniques are responsible for limited rewards out of the whole process. The study reflects upon these challenges and concludes with recommendations to improve the performance of signalized intersections along corridors with heterogeneous traffic conditions.

Operational Effects of the Displaced Partial Cloverleaf Interchange

As the roadway infrastructure in the United States evolves, transportation agencies continue to seek effective interchange alternatives that can accommodate site-specific needs, such as high through and turning volumes, or optimized traffic signal operations (by minimizing the number of traffic signal phases). In recent years, innovative interchanges such as the diverging diamond have enabled transportation agencies to explore unique designs compatible with their specific needs. This paper introduces a new innovative interchange, known as a displaced partial cloverleaf (DPC) interchange. This unique interchange is characterized by a single intersection, six free-flow movements, only four movements controlled by the solitary traffic signal, an intersection location that can be shifted, and only 12 conflict points. The flexible intersection location can help an agency improve corridor progression, eliminate conflicting queues from nearby intersections, or enhance/maintain the bridge structure without compromising the intersection operations. A microsimulation study was conducted to compare the operational performance of a DPC interchange to that of a four-quadrant type B partial cloverleaf (PARCLO B-4Q) interchange, which is very similar in layout to a DPC interchange. Results show significant decreases in experienced travel time for left-turning vehicles with the DPC. The DPC interchange is recommended as an alternative option for interchanges with very heavy left-turning onramp demand in combination with heavy crossroad demand.

Evaluation of Multiple Hardware and Software in the Loop Signal Controllers in Simulation Environment

This study evaluates two groups of methods to model traffic signal operations in microscopic simulation: hardware-in-the-loop simulation (HILS) and software-in-the-loop simulation (SILS). These methods have become standards for accurate modeling of traffic signal operations, but in spite of the large number of available options there are no studies that have conducted relevant comparative evaluations. This study bridges this gap by investigating signal timing and operational differences of these two methods in basic actuated operations of a single signalized intersection. The emphasis is given to broad examination of various platforms as opposed to more complex experiments done with individual platforms. A representative number of 65-minute simulation runs was executed for each experimental scenario. The results showed that differences between various HILS and SILS platforms are large enough that one cannot confidently switch between the platforms without affecting the final outcomes. The study confirmed previous findings about the impact of the initialization process on the simulation results, but the initialization itself does not seem to be the major source of discrepancy. Further investigation is needed to reveal role of consistency of internal NEMA-based controller logics among various controllers. These findings put a considerable dilemma/restriction on how various HILS and SILS platforms, either alone or in conjunction with other higher forms of traffic control strategies, can be used in joint fashion.