A Cellular Automaton Model for Bi-Directionnal Traffic

We investigate a cellular automaton (CA) model of traffic on a bi-directional two-lane road. Our model is an extension of the one-lane CA model of {Nagel and Schreckenberg 1992}, modified to account for interactions mediated by passing, and for a distribution of vehicle speeds. We chose values for the various parameters to approximate the behavior of real traffic. The density-flow diagram for the bi-directional model is compared to that of a one-lane model, showing the interaction of the two lanes. Results were also compared to experimental data, showing close agreement. This model helps bridge the gap between simplified cellular automata models and the complexity of real-world traffic.Comment: 4 pages 6 figures. Accepted Phys Rev

Intelligent Controlling Simulation of Traffic Flow in a Small City Network

We propose a two dimensional probabilistic cellular automata for the description of traffic flow in a small city network composed of two intersections. The traffic in the network is controlled by a set of traffic lights which can be operated both in fixed-time and a traffic responsive manner. Vehicular dynamics is simulated and the total delay experienced by the traffic is evaluated within specified time intervals. We investigate both decentralized and centralized traffic responsive schemes and in particular discuss the implementation of the {\it green-wave} strategy. Our investigations prove that the network delay strongly depends on the signalisation strategy. We show that in some traffic conditions, the application of the green-wave scheme may destructively lead to the increment of the global delay.Comment: 8 pages, 10 eps figures, Revte

A PROCEDURE FOR REAL-TIME SIGNAL CONTROL THAT CONSIDERS TRANSIT INTERFERENCE AND PRIORITY

A rule-based procedure for determining real-time signal timings at a signalized intersection is described. It incorporates the effects of the traffic interference caused by on-line loading/unloading of transit vehicles at the intersection. This procedure generates a number of short-term alternative real-time phase sequences for various levels of transit priority, based on a number of decision rules. It then evaluates these signal sequences and selects the one with the least overall cost to all traffic. The procedure is illustrated in terms of a simulated application to a critical intersection in Toronto\u27s Queen Street corridor using real data. The preliminary simulation tests indicate the potential reduction in total delay compared to fixed-time operation, which results largely from selectively ushering transit vehicles to their loading positions at strategic times and serving cross-street traffic while the transit vehicles are loading

TRAFFIC ASSIGNMENT AND SIGNAL CONTROL IN SATURATED ROAD NETWORKS

This article presents a model and a procedure for determining traffic assignment and optimizing signal timings in saturated road networks. Both queuing and congestion are explicitly taken into account in predicting equilibrium flows and setting signal split parameters for a fixed pattern of origin-to-destination trip demand. The model is formulated as a bilevel programming problem. The lower-level problem represents a network equilibrium model involving queuing explicitly on saturated links, which predicts how drivers will react to any given signal control pattern. The upper-level problem is to determine signal splits to optimize a system objective function, taking account of drivers' route choice behavior in response to signal split changes. Sensitivity analysis is implemented for the queuing network equilibrium problem to obtain the derivatives of equilibrium link flows and equilibrium queuing delays with respect to signal splits. The derivative information is then used to develop a gradient descent algorithm to solve the proposed bilevel traffic signal control problem. A numerical example is included to demonstrate the potential application of the assignment model and signal optimization procedure

TRAFFIC ASSIGNMENT AND TRAFFIC CONTROL IN GENERAL FREEWAY ARTERIAL CORRIDOR SYSTEMS

We consider a general traffic corridor consisting of two subsystems of a freeway network and a surface street network. The two systems are coupled by access ramps to provide multiple alternative routes for drivers from their origins to destinations. Each ramp can be metered to influence flow distributions in such a way that some system performance index (e.g. total travel time) is optimized, provided that each driver chooses an individual minimum cost route in response to any given ramp control. In this article we first present a bilevel programming formulation of the traffic assignment and traffic control problem in the traffic corridor system. The lower-level problem represents a traffic equilibrium model involving explicitly ramp queuing, which predicts how drivers will react to any given on-ramp control pattern. The upper-level problem is to determine ramp metering rates that optimize a system performance criterion, taking into account drivers' route choice behavior. We also present a sensitivity analysis for the queuing network equilibrium problem. Explicit expression of the derivatives of equilibrium link flows and equilibrium ramp queuing times with respect to ramp metering rates is derived. A heuristic algorithm, using the derivative information from the sensitivity analysis, is developed to solve the proposed bilevel on-ramp traffic control problem. A numerical example is provided to illustrate the bilevel control model and the solution algorithm

REAL-TIME TRAFFIC SIGNAL OPTIMIZATION WITH TRANSIT PRIORITY: RECENT ADVANCES IN THE SIGNAL PRIORITY PROCEDURE FOR OPTIMIZATION IN REAL-TIME MODEL

Real-time traffic signal optimization software was developed using object-oriented techniques based upon the SPPORT (Signal Priority Procedure for Optimization in Real Time) model. SPPORT is a rule-based model that provides specialized mechanisms for transit priority. Based upon a flexible discrete-event traffic simulator that realistically models the effects of transit operations on the general flow of traffic, and equipped with rules designed to provide effective transit priority while still giving appropriate consideration to other traffic, SPPORT generates signal timings to minimize an objective function in which transit vehicles may be weighted as deemed appropriate in relation to other traffic. In developing this software, the SPPORT model was extended to support user-defined intersection configurations, multiphase traffic signal operation, and a more advanced form of transit priority that considers both nearside and mid-block transit stop locations. The fundamental concepts of the SPPORT model and their relationships to the key components of the SPPORT software are the foci of this paper. An illustrative example and a set of simulation test results are also presented

Antioxidant and antimicrobial activities of white, green and black tea extracts

In the present study, the antioxidant and antimicrobial activities of three tea (Camellia sinensis) types (white tea — WT, green tea — GT, and black tea — BT) were compared and the relationships between total phenolic, tannin and flavonoid contents were determined. Regardless of the assays used, the highest total phenolic content (313.3±1.41 μg GAE/mg extract), total flavonoid (16.98±0.27 μg QE/mg extract) and total tannin content (266.79±2.59 μg TAE/mg extract) were determined in green tea extract, which also demonstrated the highest antioxidant capacity. Black tea extract showed the lowest phenolic content and antioxidant capacity. The EC50 value of DPPH scavenging activity was in the order of: ascorbic acid >GT>BHA>WT>BT>BHT. While the tea extracts exhibited antibacterial activity against Staphylococcus aureus, no inhibitory effects were observed against Escherichia coli and Salmonella enteritidis. All extracts exhibited antifungal activity against two afl atoxigenic moulds Aspergillus parasiticus NRRL 2999 and NRRL 465. The antibacterial activity of tea extracts decreased in the following order: GT>WT>BT DPPH scavenging activity strongly correlated with total phenolic content, reducing power, antimicrobial activity against S. aureus, A. parasiticus NRRL 2999, A. parasiticus NRRL 465 (P<0.05). These data suggest that green tea extract is more effective than white and black tea extracts as a potential source of natural antioxidants