Effects of traffic signal coordination on the safety performance of urban arterials

Urban traffic congestion and crashes have been considered by city planners as critical challenges to the economic development of the city. Traffic signal coordination, which connects a series of signals along an arterial by various coordination methodologies, has been proved as one of the most cost-effective means of reducing traffic congestion. In this regard, Metropolitan Planning Organizations (MPO) or Transportation Management Centers (TMC) have included signal timing coordination in their strategic plans. Nevertheless, concerns on the safety effects of traffic signal coordination have been continuously raised by both transportation agencies and the public. This is mainly because signal coordination may increase the travel speed along an arterial, which increases the risk and severity of traffic collisions. To date, there is neither solid evidence from the field to support the concern, nor theoretical-level models to analyze this issue. This research aims to investigate the effects of traffic signal coordination on the safety performance of urban arterials through microsimulation modeling of two traffic operational conditions: free signal operation and coordinated signals, respectively. Three urban arterials in Reno, Nevada were selected as the simulation testbed and were coded in the PTV VISSIM software. The simulated trajectory data were analyzed by the Surrogate Safety Assessment Model (SSAM) to estimate the number of traffic conflicts. Sensitivity analyses were conducted for various traffic demand levels. Results show that under unsaturated conditions, traffic signal coordination could reduce the number of conflicts in comparison with the free signal operation condition. However, under oversaturated conditions, no significant difference was found between coordinated and free signal operations. Findings from this research indicate that traffic signal coordination has the potential to reduce the risk of crashes on urban arterials under unsaturated conditions.

A Multiroute Signal Control Model considering Coordination Rate of Green Bandwidth

Oriented to characteristics of the inflow and outflow of routes in urban road network, we modified the classical fundamental green wave bandwidth model, in which separate turning green wave band is available for traffic flow from subarterials merging into an arterial, and this variable green wave band can be more flexible to service the commuting traffic. Moreover, with the analysis of the mapping characteristics of the phase coordination rate, the concept of the coordination rate of green wave bandwidth was proposed, with which as the objective function, a multiroute signal coordination control model was established, and this model is a mixed integer linear programming problem with the overall optimal coordination rate of inbound, outbound, and turning movement as the objective. Finally, a case study was given with road network in Suzhou Industrial Park, Jiangsu Province, China. From the simulation results, we can conclude that the coordinated distribution of the model proposed in this study is more stable; the fluctuation range is 0.09, which is less than that of optimization scheme in classical signal timing software Synchro, which is 0.33; and the total route delay can also be reduced by 15% compared to the current situation and 3.3% compared to Synchro optimization solution.

Safety Analysis of Signal-Coordinated Arterials with Multiple Heterogeneities

In the corresponding research available, the safety impact remains controversial in implementing signal coordination on arterials, which calls for an in-depth exploration with the appropriate statistical methods. Based on the traffic data from Ann Arbor City (Michigan, USA), the paper proposes a safety evaluation model considering the multiple heterogeneities. In terms of arterials with the coordinated signalization, modeling results imply that (1) the multivariate heterogeneity shows the strongest interaction on crash frequency, followed by the spatiotemporal and structural heterogeneities, and (2) the spatial variation is unrelated to the temporal change among crashes in the denoted traffic analysis zones (TAZs). In an attempt to alleviate the coupled crash risks along the coordinated arterials, the study emphasizes the necessity of dividing the subcontrol traffic areas in real time according to the correlative degree of crash distribution. Meanwhile, the modeling framework with multiple heterogeneities can be applied for the safety analysis of other urban roads.

Evaluating the Operational Efficiency of Two Versions of Super Diverging Diamond Interchange Design: A Case Study in Denver, Colorado

This paper aims to advance the current research on the new super diverging diamond interchange (super DDI) design by evaluating the operational efficiency using real-world locations. As part of a comprehensive research effort on improving the performance of failing service interchanges in the mountain-plains region, the study identified three interchanges (Interstate 225 and Mississippi Avenue, Interstate 25 and 120th Avenue, and Interstate 25 and Hampden Avenue) at Denver, Colorado as the potential candidates to model for future retrofit. Four interchange designs (i.e., existing CDI [conventional diamond interchange], DDI, super DDI-1, and super DDI-2) were tested in this study. The operational analysis was conducted using VISSIM and Synchro. Several microsimulation models (120 scenarios with 600 runs in total) were created with three peak hours (a.m., noon, and p.m.) for existing (the year 2020) and projected (the year 2030) traffic volumes. The study considered two simulation networks: (1) when no adjacent traffic signal exists, to determine how the four interchange designs would perform if there were no adjacent signals or they were far away from the interchange; and (2) when there are two adjacent traffic signals, to evaluate the performance of the four interchanges in a bigger corridor with signal coordination needed. An important finding is that super DDI designs outperformed DDI with adjacent signals and higher traffic demand, while DDI performed similarly to or sometimes insignificantly better than super DDI if no adjacent intersections were located in the vicinity and if the demand was lower than the DDI’s capacity.

Traffic signal coordination for Wellington Street West, Toronto, Ontario

The increasing volume of traffic in cities has a significant effect on road traffic congestion and the travel time it takes for road users to reach their destinations. Coordinating traffic signals, which is a system of light that cascade in sequence where a platoon of vehicles can travel through a continuous series of green light without stopping, can improve the driver's experience significantly. This report covers the development of a coordinated traffic signal system along Wellington Street West from Church Street to Blue Jays Way Street as part of a City of Toronto signal coordination project. The objective of this study is to improve coordination through modification of signal timing plans while maintaining reasonably minimal impacts to the side street levels of service and delays. The overall goal is to reduced travel times, delays, number of stops and fuel consumption, resulting in public benefit.

Traffic signal coordination for Wellington Street West, Toronto, Ontario

The increasing volume of traffic in cities has a significant effect on road traffic congestion and the travel time it takes for road users to reach their destinations. Coordinating traffic signals, which is a system of light that cascade in sequence where a platoon of vehicles can travel through a continuous series of green light without stopping, can improve the driver's experience significantly. This report covers the development of a coordinated traffic signal system along Wellington Street West from Church Street to Blue Jays Way Street as part of a City of Toronto signal coordination project. The objective of this study is to improve coordination through modification of signal timing plans while maintaining reasonably minimal impacts to the side street levels of service and delays. The overall goal is to reduced travel times, delays, number of stops and fuel consumption, resulting in public benefit.

Improving safety and traffic operations in urban zones with a high propensity for rear-end collisions at signalized intersections

At signalized intersections, rear-end accidents are frequently the predominant accident type. These accidents result from the combination of a lead-vehicle's decelereation and the ineffective response of the following vehicle's driver to this deceleration. The frequency and severity of rear end collisions can be reduced through traffic control and operational improvements. There are different traffic operation strategies for rear-end collision reduction like "Employ multiphase signal operation". "optimize clearance intervals" or "Restrict or eliminate turning maneuvers (including right turns on red)". In practice, the most cost-effective strategy appears to be "Employ Signal Coordination". The first objective of this research report was to use spatial analysis tools to disaggregate Toronto into 76 spatial zones (Toronto is usually divided into 158 zones). The second objective was to rank the 76 zones according to their propensity for rear-end collisions at 4-legged signalized intersections. The third objective was to demonstrate how safety can be improved through signal coordination and progression. The software package Synchro-4.00 was used to recommend improved signal coordination through optimization of cycle lenghts, splits and offsets. The coordination analysis for the 15 intersectins located in the zone with the highest propensity for rear-end collision revealed the following results. 1. Coordination was definitely not recommended for three of the intersections. 2. Coordination was probably not recommended for six of the intersections; and 3. Coordination was definitely recommended for six of the intersections. The coordinatability analysis for the 15 intersections located in the zone with the highest propensity for rear-end collisions was performed on the basis of current cycle length (based on field observations). At the nine intersection where coordination is either definitely not recommended or probably not recommended, current cycle length needs to be optimized.

Improving safety and traffic operations in urban zones with a high propensity for rear-end collisions at signalized intersections

At signalized intersections, rear-end accidents are frequently the predominant accident type. These accidents result from the combination of a lead-vehicle's decelereation and the ineffective response of the following vehicle's driver to this deceleration. The frequency and severity of rear end collisions can be reduced through traffic control and operational improvements. There are different traffic operation strategies for rear-end collision reduction like "Employ multiphase signal operation". "optimize clearance intervals" or "Restrict or eliminate turning maneuvers (including right turns on red)". In practice, the most cost-effective strategy appears to be "Employ Signal Coordination". The first objective of this research report was to use spatial analysis tools to disaggregate Toronto into 76 spatial zones (Toronto is usually divided into 158 zones). The second objective was to rank the 76 zones according to their propensity for rear-end collisions at 4-legged signalized intersections. The third objective was to demonstrate how safety can be improved through signal coordination and progression. The software package Synchro-4.00 was used to recommend improved signal coordination through optimization of cycle lenghts, splits and offsets. The coordination analysis for the 15 intersectins located in the zone with the highest propensity for rear-end collision revealed the following results. 1. Coordination was definitely not recommended for three of the intersections. 2. Coordination was probably not recommended for six of the intersections; and 3. Coordination was definitely recommended for six of the intersections. The coordinatability analysis for the 15 intersections located in the zone with the highest propensity for rear-end collisions was performed on the basis of current cycle length (based on field observations). At the nine intersection where coordination is either definitely not recommended or probably not recommended, current cycle length needs to be optimized.

An Overlapping Phase Approach to Optimize Bus Signal Priority Control under Two-Way Signal Coordination on Urban Arterials

With the consideration of the uneven traffic volume distribution at intersections on urban arterials, this paper aims to minimize the overall passenger delay (buses and private vehicles) at intersections and identify the applicable conditions of the proposed method with field data. The overlapping phase-based signal control logic and the bus priority control algorithm under two-way signal coordination on arterial roads are proposed. The vehicular capacities and occupancies for buses and passenger cars are considered in the evaluation of the method performance. A field test was carried out at two major intersections on an arterial road in Hefei, China. With the test data, the proposed method is examined and the possible influencing factors are analyzed for identifying the corresponding applicable conditions. The analysis result shows that the application of the overlapping phase helps to provide a relatively flexible signal control for the varying traffic demands at intersections. Compared to the conventional phase, it isof more practical significance to consider overlapping phase and apply bussignal priority control under two-way signal coordination according to the condition of uneven traffic volumedistribution at intersections on urban arterials. The proposed method can effectively decrease the total passenger delay at the intersections on urban arterials under certain applicable conditions. The possible factors influencing the method applicability are identified as well. It is verified that bus signal priority control under the two-way signal coordination, based on overlapping phases, is more conducive to improving traffic efficiency on urban arterials. Regarding the influencing factors and the applicability of the proposed method, the results show that not all situations are conducive to decreasing passenger delay at intersections. The proposed method should be applied under certain applicable conditions and principles in order to efficiently and effectively improve the traffic efficiency on arterial roads.